Circuit and System of Using Junction Diode as Program Selector for One-Time Programmable Devices with Heat Sink

ABSTRACT

Junction diodes fabricated in standard CMOS logic processes can be used as program selectors with at least one heat sink or heater to assist programming for One-Time Programmable (OTP) devices, such as electrical fuse, contact/via fuse, contact/via anti-fuse, or gate-oxide breakdown anti-fuse, etc. The heat sink can be at least one thin oxide area, extended OTP element area, or other conductors coupled to the OTP element to assist programming. A heater can be at least one high resistance area such as an unsilicided polysilicon, unsilicided active region, contact, via, or combined in serial, or interconnect to generate heat to assist programming. The OTP device has at least one OTP element coupled to at least one diode in a memory cell. The diode can be constructed by P+ and N+ active regions in a CMOS N well, or on an isolated active region as the P and N terminals of the diode. The isolation between P+ and the N+ active regions of the diode in a cell or between cells can be provided by dummy MOS gate, SBL, or STI/LOCOS isolations. The OTP element can be polysilicon, silicided polysilicon, silicide, polymetal, metal, metal alloy, local interconnect, metal-0, thermally isolated active region, CMOS gate, or combination thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/842,824, filed on Mar. 15, 2013 and entitled “Circuit and System ofUsing Junction Diode as Program Selector for One-Time ProgrammableDevices with Heat Sink,” which is hereby incorporated herein byreference,

The prior application U.S. patent application Ser. No. 13/842,824 is acontinuation-in-part of U.S. patent application Ser. No. 13/471,704,filed on May 15, 2012 and entitled “Circuit and System of Using JunctionDiode as Program Selector for One-Time Programmable Devices,” which ishereby incorporated herein by reference, and which claims prioritybenefit of U.S. Provisional Patent Application No. 61/609,353, filed onMar. 11, 2012 and entitled “Circuit and System of Using Junction Diodeas Program Selector for One-Time Programmable Devices,” which is herebyincorporated herein by reference.

The prior application U.S. patent application Ser. No. 13/842,824 alsoclaims priority benefit of: (i) U.S. Provisional Patent Application No.61/728,240, filed on Nov. 20, 2012 and entitled “Circuit and System ofUsing Junction Diode as Program Selector for One-Time ProgrammableDevices with Heat Sink,” which is hereby incorporated herein byreference: (ii) U.S. Provisional Patent Application No. 61/668,031,filed on Jul. 5, 2012 and entitled “Circuit and System of Using JunctionDiode as Program Selector and MOS as Read Selector for One-TimeProgrammable Devices,” which is hereby incorporated herein by reference;and (iii) U.S. Provisional Patent Application No. 61/684,800, filed onAug. 19, 2012 and entitled “Circuit and System of Using Junction Diodeas Program Selector for Metal Fuses for One-Time Programmable Devices,”which is hereby incorporated herein by reference.

The prior application U.S. patent application Ser. No. 13/471,704 is acontinuation-in-part of U.S. patent application Ser. No. 13/026,752,filed on Feb. 14, 2011 and entitled “Circuit and System of UsingJunction Diode as Program Selector for One-Time Programmable Devices,”which is hereby incorporated herein by reference, and which claimspriority benefit of (i) U.S. Provisional Patent Application No.61/375,653, filed on Aug. 20, 2010 and entitled “Circuit and System ofUsing Junction Diode As Program Selector for Resistive Devices in CMOSLogic Processes,” which is hereby incorporated herein by reference; and(ii) U.S. Provisional Patent Application No. 61/375,660, filed on Aug.20, 2010 and entitled “Circuit and System of Using Polysilicon Diode AsProgram Selector for Resistive Devices in CMOS Logic Processes,” whichis hereby incorporated herein by reference.

The prior application U.S. patent application Ser. No. 13/471,704 is acontinuation-in-part of U.S. patent application Ser. No. 13/026,656,filed on Feb. 14, 2011 and entitled “Circuit and System of UsingPolysilicon Diode As Program Selector for One-Time ProgrammableDevices,” which claims priority benefit of (i) U.S. Provisional PatentApplication No. 61/375,653, filed on Aug. 20, 2010 and entitled “Circuitand System of Using Junction Diode As Program Selector for ResistiveDevices in CMOS Logic Processes,” which is hereby incorporated herein byreference; and (ii) U.S. Provisional Patent Application No. 61/375,660,filed on Aug. 20, 2010 and entitled “Circuit and System of UsingPolysilicon Diode As Program Selector for Resistive Devices in CMOSLogic Processes,” which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to programmable memory devices, such asprogrammable resistive devices for use in memory arrays.

2. Description of the Related Art

A programmable resistive device is generally referred to a device'sresistance states that may change after means of programming. Resistancestates can also be determined by resistance values. For example, aresistive device can be a One-Time Programmable (OTP) device, such aselectrical fuse, and the programming means can apply a high voltage toinduce a high current to flow through the OTP element. When a highcurrent flows through an OTP element by turning on a program selector,the OTP element can be programmed, or burned into a high or lowresistance state (depending on either fuse or anti-fuse).

An electrical fuse is a common OTP which is a programmable resistivedevice that can be constructed from a segment of interconnect, such aspolysilicon, silicided polysilicon, silicide, metal, metal alloy, orsome combination thereof. The metal can be aluminum, copper, or othertransition metals. One of the most commonly used electrical fuses is aCMOS gate, fabricated in silicided polysilicon, used as interconnect.The electrical fuse can also be one or more contacts or vias instead ofa segment of interconnect. A high current may blow the contact(s) orvia(s) into a very high resistance state. The electrical fuse can be ananti-fuse, where a high voltage makes the resistance lower, instead ofhigher. The anti-fuse can consist of one or more contacts or vias withan insulator in between. The anti-fuse can also be a CMOS gate coupledto a CMOS body with a thin gate oxide as insulator.

The programmable resistive device can be a reversible resistive devicethat can be programmed into a digital logic value “0” or “1”repetitively and reversibly. The programmable resistive device can befabricated from phase change material, such as Germanium (Ge), Antimony(Sb), and Tellurium (Te) with composition Ge₂Sb₂Te₅ (GST-225) orGeSbTe-like materials including compositions of Indium (In), Tin (Sn),or Selenium (Se). Another phase change material can include achalcogenide material such as AgInSbTe. The phase change material can beprogrammed into a high resistance amorphous state or a low resistancecrystalline state by applying a short and high voltage pulse or a longand low voltage pulse, respectively.

Another type of reversible resistive device is a class of memory calledResistive RAM (RRAM), which is a normally insulating dielectric, but canbe made conducting through filament, defects, metal migration, etc. Thedielectric can be binary transition metal oxides such as NiO or TiO2,perovskite materials such as Sr(Zr)TiO3 or PCMO, organic charge transfercomplexes such as CuTCNQ, or organic donor-acceptor systems such as AlAlDCN. As an example, RRAM can have cells fabricated from metal oxidesbetween electrodes, such as Pt/NiO/Pt, TiN/TiOx/HfO2/TiN, TiN/ZnO/Pt, orW/TiN/SiO2/Si, etc. The resistance states can be changed reversibly anddetermined by polarity, magnitude, duration, voltage/current-limit, orthe combinations thereof to generate or annihilate conductive filaments.Another programmable resistive device similar to RRAM is a ConductiveBridge RAM (CBRAM) that is based on electro-chemical deposition andremoval of metal ions in a thin solid-state electrolyte film. Theelectrodes can be an oxidizable anode and an inert cathode and theelectrolyte can be Ag- or Cu-doped chalcogenide glass such as GeSe,Cu2S, or GeS, etc. The resistance states can be changed reversibly anddetermined by polarity, magnitude, duration, voltage/current-limit, orcombinations thereof to generate or annihilate conductive bridges. Theprogrammable resistive device can also be an MRAM (Magnetic RAM) withcells fabricated from magnetic multi-layer stacks that construct aMagnetic Tunnel Junction (MTJ). In a Spin Transfer Torque MRAM(STT-MRAM) the direction of currents applied to an MTJ determinesparallel or anti-parallel states, and hence low or high resistancestates.

A conventional programmable resistive memory cell 10 is shown in FIG. 1.The cell 10 consists of a resistive element 11 and an NMOS programselector 12. The resistive element 11 is coupled to the drain of theNMOS 12 at one end, and to a high voltage V+ at the other end. The gateof the NMOS 12 is coupled to a select signal (Sel), and the source iscoupled to a low voltage V−. When a high voltage is applied to V+ and alow voltage to V−, the resistive cell 10 can be programmed by raisingthe select signal (Sel) to turn on the NMOS 12. One of the most commonresistive elements is a silicided polysilicon, the same material andfabricated at the same time as a MOS gate. The size of the NMOS 12, asprogram selector, needs to be large enough to deliver the requiredprogram current for a few microseconds. The program current for asilicided polysilicon is normally between a few milliamps for a fusewith width of 40 nm to about 20 mA for a fuse with width about 0.6 um.As a result, the cell size of an electrical fuse using silicidedpolysilicon tends to be very large. The resistive cell 10 can beorganized as a two-dimensional array with all Sel's and V−'s in a rowcoupled as wordlines (WLs) and a ground line, respectively, and all V+'sin a column coupled as bitlines (BLs).

Another conventional programmable resistive device 20 for Phase ChangeMemory (PCM) is shown in FIG. 2( a). The PCM cell 20 has a phase changefilm 21 and a bipolar transistor 22 as program selector with P+ emitter23, N base 27, and P sub collector 25. The phase change film 21 iscoupled to the emitter 23 of the bipolar transistor 22 at one end, andto a high voltage V+ at the other. The N type base 27 of bipolartransistor 22 is coupled to a low voltage V−. The collector 25 iscoupled to ground. By applying a proper voltage between V+ and V− for aproper duration of time, the phase change film 21 can be programmed intohigh or low resistance states, depending on voltage and duration.Conventionally, to program a phase-change memory to a high resistancestate (or reset state) requires about 3V for 50 ns and consumes about300 uA of current, or to program a phase-change memory to a lowresistance state (or set state) requires about 2V for 300 ns andconsumes about 100 uA of current.

FIG. 2( b) shows a cross section of a conventional bipolar transistor22. The bipolar transistor 22 includes a P+ active region 23, a shallowN well 24, an N+ active region 27, a P type substrate 25, and a ShallowTrench Isolation (STI) 26 for device isolation. The P+ active region 23and N+ active region 27 couple to the N well 24 are the P and Nterminals of the emitter-base diode of the bipolar transistor 22, whilethe P type substrate 25 is the collector of the bipolar transistor 22.This cell configuration requires an N well 24 be shallower than the STI26 to properly isolate cells from each other and needs 3-4 more maskingsteps over the standard CMOS logic processes which makes it more costlyto fabricate.

Another programmable resistive device 20′ for Phase Change Memory (PCM)is shown in FIG. 2( c). The PCM cell 20′ has a phase change film 21′ anda diode 22′. The phase change film 21′ is coupled between an anode ofthe diode 22′ and a high voltage V+. A cathode of the diode 22′ iscoupled to a low voltage V−. By applying a proper voltage between V+ andV− for a proper duration of time, the phase change film 21′ can beprogrammed into high or low resistance states, depending on voltage andduration. The programmable resistive cell 20′ can be organized as a twodimensional array with all V−'s in a row coupled as wordline bars(WLBs), and all V+'s in a column coupled as bitlines (BLs). As anexample of use of a diode as program selector for each PCM cell as shownin FIG. 2( c), see Kwang-Jin Lee et al., “A 90 nm 1.8V 512 MbDiode-Switch PRAM with 266 MB/s Read Throughput,” InternationalSolid-State Circuit Conference, 2007, pp. 472-273. Though thistechnology can reduce the PCM cell size to only 6.8 F² (F stands forfeature size), the diode requires very complicated process steps, suchas Selective Epitaxial Growth (SEG), to fabricate, which would be verycostly for embedded PCM applications.

FIGS. 3( a) and 3(b) show several embodiments of an electrical fuseelement 80 and 84, respectively, fabricated from an interconnect. Theinterconnect serves as a particular type of resistive element. Theresistive element has three parts: anode, cathode, and body. The anodeand cathode provide contacts for the resistive element to be connectedto other parts of circuits so that a current can flow from the anode tocathode through the body. The body width determines the current densityand hence the electro-migration threshold for a program current. FIG. 3(a) shows a conventional electrical fuse element 80 with an anode 81, acathode 82, and a body 83. This embodiment has a large symmetrical anodeand cathode. FIG. 3( b) shows another conventional electrical fuseelement 84 with an anode 85, a cathode 86, and a body 87. Thisembodiment has an asymmetrical shape with a large anode and a smallcathode to enhance the electro-migration effect based on polarity andreservoir effects. The polarity effect means that the electro-migrationalways starts from the cathode. The reservoir effect means that asmaller cathode makes electro-migration easier because the smaller areahas lesser ions to replenish voids when the electro-migration occurs.The fuse elements 80, 84 in FIGS. 3( a) and 3(b) are relatively largestructures which makes them unsuitable for some applications.

FIGS. 4( a) and 4(b) show programming a conventional MRAM cell 210 intoparallel (or state 0) and anti-parallel (or state 1) by currentdirections. The MRAM cell 210 consists of a Magnetic Tunnel Junction(MTJ) 211 and an NMOS program selector 218. The MTJ 211 has multiplelayers of ferromagnetic or anti-ferromagnetic stacks with metal oxide,such as Al₂O₃ or MgO, as an insulator in between. The MTJ 211 includes afree layer stack 212 on top and a fixed layer stack 213 underneath. Byapplying a proper current to the MTJ 211 with the program selector CMOS218 turned on, the free layer stack 212 can be aligned into parallel oranti-parallel to the fixed layer stack 213 depending on the currentflowing into or out of the fixed layer stack 213, respectively. Thus,the magnetic states can be programmed and the resultant states can bedetermined by resistance values, lower resistance for parallel andhigher resistance for anti-parallel states. The resistances in state 0or 1 are about 5 KΩ or 10 KΩ, respectively, and the program currents areabout +/−100-200 μA. One example of programming an MRAM cell isdescribed in T. Kawahara, “2 Mb Spin-Transfer Torque RAM with Bit-by-BitBidirectional Current Write and Parallelizing-Direction Current Read,”International Solid-State Circuit Conference, 2007, pp. 480-481.

SUMMARY

Embodiments of programmable resistive device cells using junction diodesas program selectors are disclosed. The programmable resistive devicescan be fabricated using standard CMOS logic processes to reduce cellsize and cost.

In one embodiment, a programmable resistive device and memory can useP+/N well diodes as program selectors, where the P and N terminals ofthe diode are P+ and N+ active regions residing in an N well. The sameP+ and N+ active regions are used to create sources or drains of PMOSand NMOS devices, respectively. Advantageously, the same N well can beused to house PMOS in standard CMOS logic processes. By using P+/N welldiodes in standard CMOS processes, a small cell size can be achieved,without incurring any special processing or masks. The junction diodecan be constructed in N well in bulk CMOS or can be constructed onisolated active regions in Silicon-On-Insulator (SOI) CMOS, FinFET bulk,FinFET SOI, or similar technologies. Thus, costs can be reducedsubstantially for variously applications, such as embedded applications.

The invention can be implemented in numerous ways, including as amethod, system, device, or apparatus (including graphical user interfaceand computer readable medium). Several embodiments of the invention arediscussed below.

As a programmable resistive memory, one embodiment can, for example,include a plurality of programmable resistive cells. At least one of theprogrammable resistive cells can include a resistive element coupled toa first supply voltage line, and a diode including at least a firstactive region and a second active region isolated from the first activeregion. The first active region can have a first type of dopant and thesecond region can have a second type of dopant. The first active regioncan provide a first terminal of the diode, the second active region canprovide a second terminal of the diode, and both the first and secondactive regions can reside in a common well or on an isolated activeregion. The first and second regions can be isolated by Shallow TrenchIsolation (STI), LOCOS (LOCal Oxidation), dummy MOS gate, or SilicideBlock Layer (SBL). The first active region can also be coupled to theresistive element, and the second active region can be coupled to asecond supply voltage line. The first and second active regions can befabricated from sources or drains of CMOS devices, and in a CMOS well oron an isolated active region. The resistive element can be configured tobe programmable by applying voltages to the first and second supplyvoltage lines to thereby change the resistance into a different logicstate.

As an electronics system, one embodiment can, for example, include atleast a processor, and a programmable resistive memory operativelyconnected to the processor. The programmable resistive memory caninclude at least a plurality of programmable resistive cells forproviding data storage. Each of the programmable resistive cells caninclude at least a resistive element coupled to a first supply voltageline, and a diode including at least a first active region and a secondactive region isolated from the first active region. The first activeregion can have a first type of dopant and the second region can have asecond type of dopant. The first active region can provide a firstterminal of the diode, the second active region can provide a secondterminal of the diode, and both the first and second active regions canreside in a common well or on an isolated active region. The first andsecond regions can be isolated by Shallow Trench Isolation (STI), LOCOS(LOCal Oxidation), dummy MOS gate, or Silicide Block Layer (SBL). Thefirst active region can be coupled to the resistive element and thesecond active region can be coupled to a second supply voltage line. Thefirst and second active regions can be fabricated from sources or drainsof CMOS devices. The well can be fabricated from CMOS wells. Theisolated active region can be fabricated from SOI or FinFETtechnologies. The programmable resistive element can be configured to beprogrammable by applying voltages to the first and the second supplyvoltage lines to thereby change the resistance into a different logicstate.

As a method for providing a programmable resistive memory, oneembodiment can, for example, include at least providing a plurality ofprogrammable resistive cells, and programming a logic state into atleast one of the programmable resistive cells by applying voltages tothe first and the second voltage lines. The at least one of theprogrammable resistive cells can include at least (i) a resistiveelement coupled to a first supply voltage line, and (ii) a diodeincluding at least a first active region and a second active regionisolated from the first active region. The first active region can havea first type of dopant and the second region can have a second type ofdopant. The first active region can provide a first terminal of thediode, the second active region can provide a second terminal of thediode, and both the first and second active regions can be fabricatedfrom sources or drains of CMOS devices. Both active regions can residein a common well fabricated from CMOS wells or on an isolated activeregion. The first and second regions can be isolated by Shallow TrenchIsolation (STI), LOCOS (LOCal Oxidation), dummy MOS gate, or SilicideBlock Layer (SBL). The first active region can be coupled to theresistive element and the second active region can be coupled to asecond supply voltage line.

As a One-Time Programmable (OTP) memory, one embodiment can, forexample, include at least: a plurality of OTP cells, where at least oneof the cells includes at least: (i) an OTP element including at least aninterconnect, the OTP element being coupled to a first supply voltageline; (ii) a diode including at least a first active region and a secondactive region isolated from the first active region, where the firstactive region having a first type of dopant and a second active regionhaving a second type of dopant, the first active region providing afirst terminal of the diode, the second active region providing a secondterminal of the diode, both the first and second active regions residingin a common CMOS well or on an isolated substrate, the first activeregion coupled to the OTP element and the second active region coupledto a second supply voltage line, the first and second active regionsbeing fabricated from sources or drains of CMOS devices; and (iii) atleast one thermally conductive element, coupled to the OTP element, todissipate or generate heat. The OTP element can be configured to beprogrammable by applying voltages to the first and the second supplyvoltage lines to thereby change its logic state, and the thermallyconductive element can be configured to assist in programming of the OTPelement.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed descriptions in conjunction with the accompanying drawings,wherein like reference numerals designate like structural elements, andin which:

FIG. 1 shows a conventional programmable resistive memory cell.

FIG. 2( a) shows another conventional programmable resistive device forPhase Change Memory (PCM) using bipolar transistor as program selector.

FIG. 2( b) shows a cross section of a conventional Phase Change Memory(PCM) using bipolar transistor as program selector.

FIG. 2( c) shows another conventional Phase Change Memory (PCM) cellusing diode as program selector.

FIGS. 3( a) and 3(b) show several embodiments of an electrical fuseelement, respectively, fabricated from an interconnect.

FIGS. 4( a) and 4(b) show programming a conventional MRAM cell intoparallel (or state 0) and anti-parallel (or state 1) by currentdirections.

FIG. 5( a) shows a block diagram of a memory cell using a junction diodeaccording to the invention.

FIG. 5( b) shows a cross section of a junction diode as program selectorwith STI isolation according to one embodiment.

FIG. 5( c) shows a cross section of a junction diode as program selectorwith CMOS gate isolation according to one embodiment.

FIG. 5( d) shows a cross section of a junction diode as program selectorwith SBL isolation according to one embodiment.

FIG. 6( a) shows a cross section of a junction diode as program selectorwith dummy CMOS gate isolation in SOI technologies according to oneembodiment.

FIG. 6( a 1) shows a top view of a junction diode as program selectorwith dummy CMOS gate isolation in SOI or similar technologies accordingto one embodiment.

FIG. 6( a 2) shows a top view of a junction diode as program selectorwith Silicide Block Layer (SBL) isolation in SOI or similar technologiesaccording to one embodiment

FIG. 6( a 3) shows a top view of a programmable resistive cell having aresistive element and a program selector in one piece of an isolatedactive region with dummy gate isolation, according to one embodiment.

FIG. 6( a 4) shows a top view of a programmable resistive cell having aresistive element with a program selector in one piece of an isolatedactive region with SBL isolation, according to another embodiment.

FIG. 6( b 1) shows a 3D view of at least one junction diode as programselector with dummy CMOS gate isolation in FINFET technologies accordingto one embodiment.

FIG. 6( b 2) shows a 3D view of two junction diodes as program selectorsconstructed from two fins with an N well contact between fins in FINFETtechnologies according to another embodiment.

FIG. 6( b 3) shows a 3D view of two junction diode as program selectorsconstructed from two P type fins and an N type fins in between in FINFETtechnologies according to yet another embodiment.

FIG. 6( b 4) shows a 3D view of a junction diode as program selectorconstructed from a P type fin and an N type fin in FINFET technologiesaccording to yet another embodiment.

FIG. 6( c 1) shows a schematic of a programmable resistive cell with aPMOS for low power applications according to one embodiment.

FIG. 6( c 2) shows a schematic of a programmable resistive cell with aPMOS for low power applications according to another embodiment.

FIG. 6( c 3) shows a schematic of a programmable resistive cell with anNMOS for low power applications according to another embodiment.

FIG. 7( a) shows an electrical fuse element according to one embodiment.

FIG. 7( a 1) shows an electrical fuse element with a small body andslightly tapered structures according to another embodiment.

FIG. 7( a 2) shows an electrical fuse element using a thermallyconductive but electrically insulated heat sink in the anode accordingto another embodiment.

FIG. 7( a 3) shows an electrical fuse element with a thinner oxide asheat sink underneath the body and near the anode according to anotherembodiment.

FIG. 7( a 3 a) shows an electrical fuse element with thin oxide areas asheat sinks underneath the anode according to yet another embodiment.

FIG. 7( a 3 b) shows an electrical fuse element with thin oxide areas asheat sink near to the anode according to yet another embodiment.

FIG. 7( a 3 c) shows an electrical fuse element with an extended anodeas heat sink according to yet another embodiment.

FIG. 7( a 3 d) shows an electrical fuse element with a high resistancearea as heat generator according to one embodiment.

FIG. 7( a 4) shows an electrical fuse element with at least one notchaccording to another embodiment.

FIG. 7( a 5) shows an electrical fuse element with part NMOS metal gateand part PMOS metal gate according to another embodiment.

FIG. 7( a 6) shows an electrical fuse element with a segment ofpolysilicon between two metal gates according to another embodiment.

FIG. 7( a 7) shows a diode constructed from a polysilicon between twometal gates according to another embodiment.

FIG. 7( a 8) shows a 3D view of a metal fuse element constructed from acontact and a metal segment, according to one embodiment.

FIG. 7( a 9) shows a 3D view of a metal fuse element constructed from acontact, two vias, and segment(s) of metal 2 and metal 1, according toanother embodiment.

FIG. 7( a 10) shows a 3D view of a metal fuse element constructed from 3contacts, segment(s) of metal gate and metal-1, according to yet anotherembodiment.

FIG. 7( b) shows a top view of an electrical fuse coupled to a junctiondiode with STI isolation in four sides.

FIG. 7( c) shows a top view of an electrical fuse coupled to a junctiondiode with STI isolation in two sides and dummy CMOS isolation inanother two sides.

FIG. 7( d) shows a top view of an electrical fuse coupled to a junctiondiode with dummy CMOS isolation in four sides.

FIG. 7( e) shows a top view of an electrical fuse coupled to a junctiondiode with Silicide Block Layer isolation in four sides.

FIG. 7( f) shows a top view of an abutted contact coupled between aresistive element, P terminal of a junction diode, and metal in a singlecontact.

FIG. 7( g) shows a top view of an electrical fuse coupled to a junctiondiode with dummy CMOS gate isolation between P+/N+ of a diode andadjacent cells.

FIG. 7( h) shows a top view of a programmable resistive cell coupled toa junction diode with dummy CMOS gate isolation between P+/N+ and haslarge contacts.

FIG. 8( a) shows a top view of a metal fuse coupled to a junction diodewith dummy CMOS gate isolation.

FIG. 8( b) shows a top view of a metal fuse coupled to a junction diodewith 4 cells sharing one N well contact in each side.

FIG. 8( c) shows a top view of a via1 fuse coupled to a junction diodewith 4 cells sharing one N well contact in each side.

FIG. 8( d) shows a top view of a two-dimensional array of via1 fusesusing P+/N well diodes.

FIG. 9( a) shows a cross section of a programmable resistive device cellusing phase-change material as a resistive element, with buffer metalsand a P+/N well junction diode, according to one embodiment.

FIG. 9( b) shows a top view of a PCM cell using a P+/N well junctiondiode as program selector in accordance with one embodiment.

FIG. 10 shows one embodiment of an MRAM cell using diodes as programselectors in accordance with one embodiment.

FIG. 11( a) shows a top view of an MRAM cell with an MTJ as a resistiveelement and with P+/N well diodes as program selectors in standard CMOSprocesses in accordance with one embodiment.

FIG. 11( b) shows another top view of an MRAM cell with an MTJ as aresistive element and with P+/N well diodes as program selectors in ashallow well CMOS process in accordance with another embodiment.

FIG. 12( a) shows one embodiment of a three-terminal 2×2 MRAM cell arrayusing junction diodes as program selectors and the condition to programthe upper-right cell into 1 in accordance with one embodiment.

FIG. 12( b) shows alternative conditions to program the upper-right cellinto 1 in a 2×2 MRAM array in accordance with one embodiment.

FIG. 13( a) shows one embodiment of a three-terminal 2×2 MRAM cell arrayusing junction diodes as program selectors and the condition to programthe upper-right cell into 0 in accordance with one embodiment.

FIG. 13( b) shows alternative conditions to program the upper-right cellinto 0 in a 2×2 MRAM array in accordance with one embodiment.

FIGS. 14( a) and 14(b) show one embodiment of programming 1 and 0 intothe upper-right cell, respectively, in a two-terminal 2×2 MRAM cellarray in accordance with one embodiment.

FIG. 15 shows a portion of a programmable resistive memory constructedby an array of n-row by (m+1)-column single-diode-as-program-selectorcells and n wordline drivers in accordance with one embodiment.

FIG. 16( a) shows a portion of a programmable resistive memoryconstructed by an array of 3-terminal MRAM cells according to oneembodiment.

FIG. 16( b) shows another embodiment of constructing a portion of MRAMmemory with 2-terminal MRAM cells.

FIGS. 17( a), 17(b), and 17(c) show three other embodiments ofconstructing reference cells for differential sensing.

FIG. 18( a) shows a schematic of a wordline driver circuit according toone embodiment.

FIG. 18( b) shows a schematic of a bitline circuit according to oneembodiment.

FIG. 18( c) shows a portion of memory with an internal power supply VDDPcoupled to an external supply VDDPP and a core logic supply VDD throughpower selectors.

FIG. 19( a) shows one embodiment of a schematic of a pre-amplifieraccording to one embodiment.

FIG. 19( b) shows one embodiment of a schematic of an amplifieraccording to one embodiment.

FIG. 19( c) shows a timing diagram of the pre-amplifier and theamplifier in FIGS. 19( a) and 19(b), respectively.

FIG. 20( a) shows another embodiment of a pre-amplifier, similar to thepre-amplifier in FIG. 18( a).

FIG. 20( b) shows level shifters according to one embodiment.

FIG. 20( c) shows another embodiment of an amplifier with current-mirrorloads.

FIG. 20( d) shows another embodiment of a pre-amplifier with two levelsof PMOS pullup stacked so that all core devices can be used.

FIG. 20( e) shows another embodiment of a pre-amplifier with anactivation device for enabling.

FIG. 21( a) depicts a method of programming a programmable resistivememory in a flow chart according to one embodiment.

FIG. 21( b) depicts a method of reading a programmable resistive memoryin a flow chart according to one embodiment.

FIG. 22 shows a processor system according to one embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments disclosed herein use a P+/N well junction diode as programselector for a programmable resistive device. The diode can comprise P+and N+ active regions on an N well. Since the P+ and N+ active regionsand N well are readily available in standard CMOS logic processes, thesedevices can be formed in an efficient and cost effective manner. Forstandard Silicon-On-Insulator (SOI), FinFET, or similar technologies,isolated active regions can be used to construct diodes as programselectors or as programmable resistive elements. There are no additionalmasks or process steps to save costs. The programmable resistive devicecan also be included within an electronic system.

FIG. 5( a) shows a block diagram of a memory cell 30 using at least ajunction diode according to one embodiment. In particular, the memorycell 30 includes a resistive element 30 a and a junction diode 30 b. Theresistive element 30 a can be coupled between an anode of the junctiondiode 30 b and a high voltage V+. A cathode of the junction diode 30 bcan be coupled to a low voltage V−. In one implementation, the memorycell 30 can be a fuse cell with the resistive element 30 a operating asan electrical fuse. The junction diode 30 b can serve as a programselector. The junction diode can be constructed from a P+/N well instandard CMOS processes using a P type substrate or on an isolatedactive region in an SOI or FinFET technologies. The P+ and N+ activeregions serve as the anode and cathode of the diode are the sources ordrains of CMOS devices. The N well is a CMOS well to house PMOS devices.Alternatively, the junction diode can be constructed from N+/P well intriple-well or CMOS processes using an N type substrate. The coupling ofthe resistive element 30 a and the junction diode 30 b between thesupply voltages V+ and V− can be interchanged. By applying a propervoltage between V+ and V− for a proper duration of time, the resistiveelement 30 a can be programmed into high or low resistance states,depending on voltage and duration, thereby programming the memory cell30 to store a data value (e.g., bit of data). The P+ and N+ activeregions of the diode can be isolated by using a dummy CMOS gate, ShallowTrench Isolation (STI) or Local Oxidation (LOCOS), or Silicide BlockLayer (SBL).

Electrical fuse cell can be used as an example to illustrate the keyconcepts according to one embodiment. FIG. 5( b) shows a cross sectionof a diode 32 using a P+/N well diode as program selector with ShallowTrench Isolation (STI) isolation in a programmable resistive device. P+active region 33 and N+ active region 37, constituting the P and Nterminals of the diode 32 respectively, are sources or drains of PMOSand NMOS in standard CMOS logic processes. The N+ active region 37 iscoupled to an N well 34, which houses PMOS in standard CMOS logicprocesses. P substrate 35 is a P type silicon substrate. STI 36 isolatesactive regions for different devices. A resistive element (not shown inFIG. 5( b)), such as electrical fuse, can be coupled to the P+ region 33at one end and to a high voltage supply V+ at the other end. To programthis programmable resistive device, a high voltage is applied to V+, anda low voltage or ground is applied to the N+ region 37. As a result, ahigh current flows through the fuse element and the diode 32 to programthe resistive device accordingly.

FIG. 5( c) shows a cross section of another embodiment of a junctiondiode 32′ as program selector with dummy CMOS gate isolation. ShallowTrench Isolation (STI) 36′ provides isolation among active regions. Anactive region 31′ is defined between STI 36′, where the N+ and P+ activeregions 37′ and 33′ are further defined by a combination of a dummy CMOSgate 39′, P+ implant layer 38′, and N+ implant (the complement of the P+implant 38′), respectively, to constitute the N and P terminals of thediode 32′. The dummy CMOS gate 39′ is a CMOS gate fabricated in standardCMOS process. The width of dummy gate 39′ is preferably close to theminimum gate width of a CMOS gate. The diode 32′ is fabricated as aPMOS-like device with 37′, 39′, 33′, and 34′ as source, gate, drain, andN well, except that the source 37′ is covered by an N+ implant, ratherthan a P+ implant 38′. The dummy MOS gate 39′, preferably biased at afixed voltage, only serves for isolation between P+ active region 33′and N+ active region 37′ during fabrication. The N+ active 37′ iscoupled to an N well 34′, which houses PMOS in standard CMOS logicprocesses. P substrate 35′ is a P type silicon substrate. A resistiveelement (not shown in FIG. 5( c)), such as electrical fuse, can becoupled to the P+ region 33′ at one end and to a high voltage supply V+at the other end. To program this programmable resistive device, a highvoltage is applied to V+, and a low voltage or ground is applied to theN+ active region 37′. As a result, a high current flows through the fuseelement and the diode 32′ to program the resistive device accordingly.This embodiment is desirable for isolation for small size and lowresistance.

FIG. 5( d) shows a cross section of another embodiment of a junctiondiode 32″ as program selector with Silicide Block Layer (SBL) isolation.FIG. 5( d) is similar to 5(c), except that the dummy CMOS gate 39″ inFIG. 5( c) is replaced by SBL 39″ in FIG. 5( d) to block a silicidegrown on the top of active region 31″. Without a dummy MOS gate or aSBL, the N+ and P+ active regions would be undesirably electricallyshorted by a silicide on the surface of the active region 31″.

FIG. 6( a) shows a cross section of another embodiment of a junctiondiode 32″ as a program selector in Silicon-On-Insulator (SOI), FinFET,or similar technologies. In SOI technologies, the substrate 35″ is aninsulator such as SiO₂ or similar material with a thin layer of silicongrown on top. All NMOS and PMOS are in active regions isolated by SiO₂or similar material to each other and to the substrate 35″. An activeregion 31″ is divided into N+ active regions 37″, P+ active region 33″,and bodies 34″ by a combination of a dummy CMOS gate 39″, P+ implant38″, and N+ implant (the complement of P+ implant 38″). Consequently,the N+ active regions 37″ and P+ active region 33″ constitute the N andP terminals of the junction diode 32″. The N+ active regions 37″ and P+active region 33″ can be the same as sources or drains of NMOS and PMOSdevices, respectively, in standard CMOS processes. Similarly, the dummyCMOS gate 39″ can be the same CMOS gate fabricated in standard CMOSprocesses. The dummy MOS gate 39″, which can be biased at a fixedvoltage, only serves for isolation between P+ active region 33″ and N+active region 37″ during fabrication. The width of the dummy MOS gate39″ can vary but can, in one embodiment, be close to the minimum gatewidth of a CMOS gate. The N+ active regions 37″ can be coupled to a lowvoltage supply V−. A resistive element (not shown in FIG. 6( a)), suchas an electrical fuse, can be coupled to the P+ active region 33″ at oneend and to a high voltage supply V+ at the other end. To program theelectrical fuse cell, a high and a low voltages are applied to V+ andV−, respectively, to conduct a high current flowing through theresistive element and the junction diode 32″ to program the resistivedevice accordingly. Other embodiments of isolations in CMOS bulktechnologies, such as dummy MOS gate, or SBL in one to four (1-4) or anysides or between cells, can be readily applied to CMOS SOI technologiesaccordingly.

FIG. 6( a 1) shows a top view of one embodiment of a junction diode 832,corresponding to the cross section as shown in FIG. 6( a), constructedfrom an isolated active region as a program selector inSilicon-On-Insulator (SOI), FinFET, or similar technologies. One activeregion 831 is divided into N+ active regions 837, P+ active region 833,and bodies underneath dummy gate 839 by a combination of a dummy CMOSgate 839, P+ implant 838, and N+ implant (the complement of P+ implant838). Consequently, the N+ active regions 837 and P+ active region 833constitute the N and P terminals of the junction diode 832. The N+active region 837 and P+ active region 833 can be the same as sources ordrains of NMOS and PMOS devices, respectively, in standard CMOSprocesses. Similarly, the dummy CMOS gate 839 can be the same CMOS gatefabricated in standard CMOS processes. The dummy MOS gate 839, which canbe biased at a fixed voltage, only serves for isolation between P+active region 833 and N+ active region 837 during fabrication. The N+active region 837 can be coupled to a low voltage supply V−. A resistiveelement (not shown in FIG. 6( a 1)), such as an electrical fuse, can becoupled to the P+ active region 833 at one end and to a high voltagesupply V+ at the other end. To program the resistive element, high and alow voltages are applied to V+ and V−, respectively, to conduct a highcurrent flowing through the resistive element and the junction diode 832to program the resistive element accordingly. Other embodiments ofisolations in CMOS bulk technologies, such as dummy MOS gate, or SBL inone to four (1-4) or any sides or between cells, can be readily appliedto CMOS SOI technologies accordingly.

FIG. 6( a 2) shows a top view of one embodiment of a diode 832′constructed from an isolated active region as a program selector in anSOI, FinFET, or similar technologies. This embodiment is similar to thatin FIG. 6( a 1), except that SBL is used instead of a dummy gate forisolation. An active region 831′ is on an isolated substrate that iscovered by P+ 838′ and N+ 835′ implant layers. The P+ 838′ and N+ 835′are separated with a space D and a Silicide Block Layer (SBL) 839′covers the space and overlap into both P+ 838′ and N+ 835′ regions. TheP+ 838′ and N+ 835′ regions serve as the P and N terminals of a diode,respectively. The space regions can be doped with slightly P, N, orunintentionally doped. The space D and/or the doping level in the spaceregions can be used to adjust the breakdown or leakage of the diode832′. The diode constructed in an isolated active region can be oneside, instead of two sides as is shown in FIG. 6( a 2) or in anotherembodiment.

FIG. 6( a 3) shows a top view of one embodiment of a fuse cell 932constructed from a fuse element 931-2, a diode 931-1 as program selectorin one piece of an isolated active region, and a contact area 931-3.These elements/regions (931-1, 931-2, and 931-3) are all isolated activeregions built on the same structure to serve as a diode, fuse element,and contact area of a fuse cell 932. The isolated active region 931-1 isdivided by a CMOS dummy gate 939 into regions 933 and 937 that arefurther covered by P+ implant 938 and N+ implant (the complement of theP+ implant 938) to serve as P and N terminals of the diode 931-1. The P+933 is coupled to a fuse element 931-2, which is further coupled to thecontact area 931-3. The contact area 931-3 and the contact area forcathode of the diode 931-1 can be coupled to V+ and V− supply voltagelines, respectively, through a single or plural of contacts. When highand low voltages are applied to V+ and V−, respectively, a high currentcan flow through the fuse element 931-2 to program the fuse into a highresistance state. In one implementation, the fuse element 931-2 can beall N or all P. In another implementation, the fuse element 931-2 can behalf P and half N so that the fuse element can behave like areverse-biased diode during read, when the silicide on top is depletedafter program. If there is no silicide available, the fuse element931-2, which is an OTP element, can be constructed as N/P or P/N diodesfor breakdown in the forward or reverse biased condition. In thisembodiment, the OTP element can be coupled directly to a diode asprogram selector without any contacts in between. Thus, the cell areacan be small and its cost can be relatively low.

FIG. 6( a 4) shows a top view of one embodiment of a fuse cell 932′constructed from a fuse element 931′-2, a diode 931′ as program selectorin one piece of an isolated active region, and a contact area 931′-3.These elements/regions (931′-1, 931′-2, and 931′-3) are all isolatedactive regions built on the same structure to serve as a diode, fuseelement, and contact area of a fuse cell 932′. The isolated activeregion 931′-1 is divided by a Silicide Block Layer (SBL) in 939′ toregions 933′ and 937′ that are further covered by P+ implant 938′ and N+implant 935′ to serve as P and N terminals of the diode 931′. The P+933′ and N+ 937′ regions are separated with a space D, and an SBL 939′covers the space and overlaps into both regions. The space D and/or thedoping level in the space region can be used to adjust the breakdownvoltage or leakage current of the diode 931′. The P+ 933′ is coupled toa fuse element 931′-2, which is further coupled to the contact area931′-3. The contact area 931′-3 and the contact area for the cathode ofthe diode 931′-1 can be coupled to V+ and V− supply voltage lines,respectively, through a single or plural of contacts. When high and lowvoltages are applied to V+ and V−, respectively, a high current can flowthrough the fuse element 931′-2 to program the fuse into a highresistance state. In one implementation, the fuse element 931′-2 can beall N or all P. In another implementation, the fuse element 931′-2 canbe half P and half N so that the fuse element can behave like areverse-biased diode during read, when the silicide on top is depletedafter program. If there is no silicide available, the fuse element931′-2, which is an OTP element, can be constructed as N/P or P/N diodesfor breakdown in the forward or reverse biased condition. In thisembodiment, the OTP element can be coupled directly to a diode asprogram selector without any contacts in between. Thus, the cell areacan be small and the costs can be low

FIG. 6( b 1) shows a cross section of another embodiment of at least onediode 45 as program selector in FinFET technologies. FinFET refers to afin-based, multigate transistor. FinFET technologies are similar to theconventional CMOS except that thin and tall silicon islands can beraised above the silicon substrate to serve as the bulks of CMOSdevices. The bulks are divided into source, drain, and channel regionsby polysilicon or non-aluminum metal gates like in the conventionalCMOS. The primary difference is that the MOS devices are raised abovethe substrate so that channel widths are related to the height of theislands, though the direction of current flow is still in parallel tothe surface. In an example of FinFET technology shown in FIG. 6( b 1),the silicon substrate 35 is an epitaxial layer built on top of aninsulator like SOI or a bulk silicon substrate. The silicon substrate 35can then be etched into several tall rectangular islands 31-1, 31-2, and31-3. With proper gate oxide and field oxide grown, the islands 31-1,31-2, and 31-3 can be patterned with MOS gates 39-1, 39-2, and 39-3,respectively, to cover both sides of raised islands 31-1, 31-2, and 31-3and to define source and drain regions. In one embodiment, the sourceand drain regions formed at the islands 31-1, 31-2, and 31-3 are thenfilled with silicon/SiGe called extended source/drain regions, such as40-1 and 40-2, so that the combined source or drain areas can be largeenough to allow contacts. The extended source/drain can be fabricatedfrom polysilicon, polycrystalline Si/SiGe, lateral epitaxial growthsilicon/SiGe, or Selective Epixatial Growth (SEG) of Silicon/SiGe, etc.The extended source/drain regions 40-1 and 40-2, or other types ofisolated active regions, can be grown or deposited to the sidewall orthe end of the fins. The fill 40-1 and 40-2 areas in FIG. 6( b 1) arefor illustrative purpose to reveal the cross section and can, forexample, be filled up to the surface of the islands 31-1, 31-2, and31-3. In this embodiment, active regions 33-1,2,3 and 37-1,2,3 arecovered by a P+ implant 38 and N+ implant (the complement of P+ implant38), respectively, rather than all covered by P+ implant 38 as PMOS inthe conventional FinFET, to constitute the P and N terminals of thediode 45. The N+ active regions 37-1,2,3 can be coupled to a low voltagesupply V−. At least one resistive element (not shown in FIG. 6( b 1)),such as an electrical fuse, can be coupled to the P+ active region33-1,2,3 at one end and to a high voltage supply V+ at the other end. Toprogram the electrical fuse, high and low voltages are applied betweenV+ and V−, respectively, to conduct a high current flowing through theresistive element and the diode 45 to program the resistive deviceaccordingly. Other embodiments of isolations in CMOS bulk technologies,such as STI, dummy MOS gate or SBL, can be readily applied to FinFETtechnologies accordingly. The three fins 31-1, 31-2, and 31-3 can beconstructed as 1 to 3 diodes as program selector(s). The diodes as aprogram selector can be constructed from any number of fins in otherembodiment. There can be a plurality of dummy MOS gates across one finto create more diodes per fin in another embodiment. If there are twodummy MOS gates across one fin and two fins are used to construct aprogram selector in a programmable resistive cell, the program selectorcan be four times the driving capabilities of a single diode.

FIG. 6( b 2) shows a 3D view of two diodes 45′ as program selectors intwo fin structures and one common contact, according to one embodiment.Two fins, 31′-1 and 31′-2, are built on a substrate 35′ inside an N well36′ with P+ implants 38′-1 and 38′-2 covering the fins 31′-1 and 31′-2,respectively. After the fins are fabricated, a layer of dielectric 33′covers the two fins 31′-1 and 31′-2 to provide insulation for buildingfurther upper layers of interconnects. A contact hole 34′ can be builtby etching the dielectric layer 33′ into the substrate 35′, andimplanted with an N+ dopant. Then, the contact 34′ can be filled with atleast one conductive material (i.e., silicon, polysilicon, SiGe, ormetal) to act as an N well tap. The P+ regions 31′-1 and 31′-2 serve asthe anodes of two diodes, while the contact 34′ with an N+ region on thesubstrate serves as a common cathode. In this embodiment, a diode can becreated in only one fin pitch. The P+ regions 31′-1 and/or 31′-2 can bebuilt with dummy gates as shown in FIG. 6( b 1) to further increase thediodes' performance.

FIG. 6( b 3) shows a 3D view of two diodes 45″ as program selectors inthree fin structures, according to yet another embodiment. Two fins,31″-1 and 31″-3, are built on a substrate 35″ inside an N well 36″ withP+ implants 38″-1 and 38″-2 covering the fins 31″-1 and 31″-3,respectively. The P+ region 31″-1 and 31″-3 serve as the anodes of twodiodes, while the N+ region 31″-2 serves as the common cathode. In thisembodiment, a diode can be created in only one and a half fin pitch. TheN+ region 31″-2 can be placed between any number of P+ regions to serveas a common cathode in other embodiment. The P+ regions 31″-1 and/or31″-2 can be built with dummy gates as shown in FIG. 6( b 1) to furtherincrease the diodes' performance.

FIG. 6( b 4) shows a 3D view of one diode 45′″ as a program selector intwo fin structures, according to yet another embodiment. Two fins, 31″-1and 31″-2, are built on a substrate 35″ inside an N well 36″ with a P+implant 38″ and an N+ implant 37′″ covering the fins 31′″-1 and 31′″-2,respectively. The P+ region 31′″-1 serves as the anodes of the diode45′″, while the N+ region 31′″-2 serves as the cathode. In thisembodiment, a diode can be created in two fin pitches. The P+ region31′″-1 can be built with dummy gates as shown in FIG. 6( b 1) to furtherincrease the diodes' performance.

FIG. 6( c 1) shows a programmable resistive device cell 75 for lowvoltage and low power applications. If an I/O voltage supply of a chipis down to 1.2V, the diode's high turn-on voltage 0.7V as read/programselector can hurt the read margin. Therefore, a MOS can be used as readselector in the cell for better read operations in another embodiment.The programmable resistive cell 75 has a programmable resistive element76, a diode 77 as program selector, and a MOS 72 as read selector. Theanode of the diode 77 (node N) is coupled to the drain of the MOS 72.The cathode of the diode 77 is coupled to the source of the MOS 72 asSelect line (SL). The programmable resistive element 76 is coupledbetween node N and a high voltage V+. By applying a proper voltagebetween V+ and SL for a proper duration of time, the programmableresistive element 76 can be programmed into high or low resistancestates, depending on voltage/current and duration. The diode 77 can be ajunction diode constructed from a P+ active region on N well and an N+active region on the same N well as the P and N terminals of a diode,respectively. In another embodiment, the diode 77 can be a diodeconstructed from a polysilicon structure with two ends implanted by P+and N+, respectively. The P or N terminal of either junction diode orpolysilicon diode can be implanted by the same source or drain implantin CMOS devices. Either the junction diode or polysilicon diode can bebuilt in standard CMOS processes without any additional masks or processsteps.

The MOS 72 is for reading the programmable resistive element 76. Turningon a MOS in linear mode can have a lower voltage drop than a diode's forlow voltage operations. To turn on the diode 77, the cathode of thediode can be set to low for the selected row during write, i.e.,˜(Wr*Sel) in one embodiment. To turn on the MOS 72, the gate of the MOScan be set to low for the selected row during read, i.e., ˜(Rd*Sel) inone embodiment. If the program voltage is VDDP=2.5V and core voltage forread is VDD=1.0V, the selected and unselected SLs for program can be 0and 2.5V, respectively. The SLs can be all set to 1.0V for read. Theselected and unselected WLBs for read can be 0 and 1.0V, respectively.The programmable resistive memory cell 75 can be organized as atwo-dimensional array with all V+'s in the same columns coupled togetheras bitlines (BLs) and all MOS gates and sources in the same rows coupledtogether as wordline bars (WLBs) and Source Lines (SLs), respectively.

FIG. 6( c 2) shows a schematic of another programmable resistive cellaccording to another embodiment. FIG. 6( c 2) is similar to FIG. 6( c 1)except that the placement of the resistive element and diode/MOS areinterchanged. V+'s of the cells in the same row can be coupled to asource line (SL) that can be set to VDDP for program and VDD for read.V−'s of the cells in the same column can be coupled as a bitline (BL)and further coupled to a sense amplifier for read and set to ground forprogram. The gates of the MOS in the same row can be coupled to awordline bar (WLB) that can be set to low when selected during read,i.e., ˜(Rd*Sel), in one embodiment. Alternatively, the source of the MOScan be coupled to a fixed voltage, such as Vdd, in another embodiment.

FIG. 6( c 3) shows a schematic of another programmable resistive cellaccording to another embodiment. FIG. 6( c 3) is similar to FIG. 6( c 1)except that the PMOS is replaced by an NMOS. V+'s of the cells in thesame column can be coupled as a bitline (BL) that can be coupled to VDDPfor program and coupled to a sense amplifier for read. The cathodes ofthe diode and the sources of the MOS in the same row can be coupled as asource line (SL). The SL can be set to ground when selected for read orprogram. The gates of the MOS in the same row can be coupled as awordline (WL) that can be set high when selected for read, i.e., Rd*Sel,in one embodiment. Alternatively, the source of the MOS can be coupledto a fixed voltage, such as ground, in another embodiment.

FIGS. 6( a), 6(a 1)-6(a 4), 6(b 1)-6(b 4), and 6(c 1)-6(c 3) showsvarious schemes of constructing diodes as program selector and/or OTPelement in a fully or partially isolated active region. A diode asprogram selector can be constructed from an isolated active region suchas in SOI or FINFET technologies. The isolated active region can be usedto construct a diode with two ends implanted with P+ and N+, the sameimplants as the source/drain implants of CMOS devices, to serve as twoterminals of a diode. A dummy CMOS gate or silicide block layer (SBL)can be used for isolation and to prevent shorting of the two terminals.In the SBL isolation, the SBL layer can overlap into the N+ and P+implant regions and the N+ and P+ implant regions can be separated witha space. The width and/or the doping level in the space region can beused to adjust the diode's breakdown voltage or leakage currentaccordingly. A fuse as OTP element can also be constructed from anisolated active region. Since the OTP element is thermally isolated, theheat generated during programming cannot be dissipated easily so thatthe temperature can be raised higher to accelerate programming. The OTPelement can have all N+ or all P+ implant. If there is a silicide on topof the active region, the OTP element can have part N+ and part P+implants so that the OTP element can behave like a reverse biased diodeduring read, such as when the silicide is depleted after OTP programmingin one embodiment. If there is no silicide on top, the OTP element canhave part N+ and part P+ implants as a diode to be breakdown during OTPprogramming in another embodiment. In either case, the OTP element ordiode can be constructed on the same structure of an isolated activeregion to save area. In an SOI or FinFET SOI technology, an activeregion can be fully isolated from the substrate and from other activeregions by SiO2 or similar material. Similarly, in a FINFET bulktechnology, an active region can be fully isolated from the substrateand partially isolated from each other by using extended source/drainregions coupled between fin structures without any additional masks.

FIG. 7( a) shows a top view of an electrical fuse element 88 accordingto one embodiment. The electrical fuse element 88 can, for example, beused as the resistive element 31 a illustrated in FIG. 5( a). Theelectrical fuse element 88 includes an anode 89, a cathode 80, and abody 81. In this embodiment, the electrical fuse element 88 is a barshape with a small anode 89 and cathode 80 to reduce area. In anotherembodiment, the width of the body 81 can be about the same as the widthof cathode or anode. The width of the body 81 can be very close to theminimum feature width of the interconnect. The anode 89 and cathode 80may protrude from the body 81 to make contacts. The contact number canbe one (1) for both the anode 89 and the cathode 80 so that the area canbe very small. However, the contact area for anode 89 is often madelarger so that the anode 89 can resist electro-migration more than thecathode 80. In one embodiment, the fuse body 81 can have about 0.5-8squares, namely, the length to width ratio is about 0.5-to-8, to makeefficient use of (e.g., optimize) cell area and program current. In oneembodiment, the fuse body 81 can have about 2-6 squares, namely, thelength to width ratio is about 2-to-6, to efficiently utilize cell areaand program current. In yet another embodiment, the narrow fuse body 81can be bent to make the length longer between the wide anode and cathodeareas to efficiently utilize cell area and program current. The fuseelement 88 has a P+ implant 82 covering part of the body 81 and thecathode 80, while an N+ implant over the rest of area. This embodimentmakes the fuse element 88 behave like a reverse biased diode to increaseresistance after being programmed, such as when silicide on top isdepleted by electro-migration, ion diffusion, silicide decomposition,and other effects. It is desirable to make the program voltagecompatible with the I/O voltages, such as 3.3V, 2.5V, or 1.8V, for easeof use without the needs of building charge pumps. The program voltagepin can also be shared with at least one of the standard I/O supplyvoltage pins. In one embodiment, to make the cell small while reducingthe contact resistance in the overall conduction path, the number ofcontacts in the OTP element or diode can be no more than two (<=2), in asingle cell. Similarly, in another embodiment, the contact size of theOTP element or diode can be larger than at least one contact outside ofthe memory array. The contact enclosure can be smaller than at least onecontact enclosure outside of the memory array in yet another embodiment.

FIG. 7( a 1) shows a top view of an electrical fuse structure 88′ with asmall body 81′-1 and at least one slightly tapered structures 81′-2and/or 81′-3 according to another embodiment. The electrical fuseelement 88′ can, for example, be used as the resistive element 31 aillustrated in FIG. 5( a). The electrical fuse element 88′ includes ananode 89′, a cathode 80′, body 81′-1, and tapered structures 81′-2 and81′-3. The body 81′-1 can include a small rectangular structure coupledto at least one tapered structures 81′-2 and/or 81′-3, which are furthercoupled to cathode 80′ and anode 89′, respectively. The length (L) andwidth (W) ratio of the body 81′-1 is typically between 0.5 and 8. Inthis embodiment, the electrical fuse element 88′ is substantially a barshape with a small anode 89′ and cathode 80′ to reduce area. The anode89′ and cathode 80′ may protrude from the body 81-1′ to make contacts.The contact number can be one (1) for both the anode 89′ and the cathode80′ so that the area can be very small. The contact can be larger thanat least one contact outside of the memory array in another embodiment.The contact enclosure can be smaller than at least one contact enclosureoutside of the memory array in yet another embodiment. P+ implant layer82′ covers part of the body and N+ implant layer (the complement of P+)covers the other part so that the body 81′-1 and taped structure 81′-2can behave like a reverse biased diode to enhance resistance ratioduring read, such as when silicide on top is depleted after program.

FIG. 7( a 2) shows a top view of an electrical fuse element 88″according to another embodiment. The electrical fuse element 88″ issimilar to the one shown in FIG. 7( a) except using a thermallyconductive but electrically insulated heat sink coupled to the anode.The electrical fuse element 88″ can, for example, be used as theresistive element 31 a illustrated in FIG. 5( a). The electrical fuseelement 88″ can include an anode 89″, a cathode 80″, a body 81″, and anN+ active region 83″. The N+ active region 83″ on a P type substrate iscoupled to the anode 89″ through a metal 84″. In this embodiment, the N+active region 83″ is electrically insulated from the conduction path(i.e., N+/P sub diode is reverse biased), but thermally conductive tothe P substrate, and can serve as a heat sink. In other embodiment, theheat sink can be coupled to the anode 89″ directly without using anymetal or interconnect, and can be close to or underneath the anode. Theheat sink can also be coupled to the body, cathode, or anode in part orall of the fuse element in other embodiments. This embodiment of heatsink can create a steep temperature gradient to accelerate programming.

FIG. 7( a 3) shows a top view of an electrical fuse element 88′″according to another embodiment. The electrical fuse element 88′″ issimilar to the one shown in FIG. 7( a) except a thinner oxide region83′″ which serves as a heat sink underneath the body 81″ and near theanode 89′″. The electrical fuse element 88′″ can, for example, be usedas the resistive element 31 a illustrated in FIG. 5( a). The electricalfuse element 88′″ includes an anode 89′″, a cathode 80′″, a body 81′″,and an active region 83′″ near the anode 89′″. The active region 83′″underneath the fuse element 81′″ makes the oxide thinner in the areathan the other (i.e., thin gate oxide instead of thick STI oxide). Thethinner oxide above the active region 83′″ can dissipate heat faster tocreate a temperature gradient to accelerate programming. In otherembodiments, the thin oxide area 83′″ can be placed underneath thecathode, body, or anode in part or all of a fuse element as a heat sink.

FIG. 7( a 3 a) shows a top view of an electrical fuse element 198according to another embodiment. The electrical fuse element 198 issimilar to the one shown in FIG. 7( a) except thinner oxide regions 193are placed in two sides of the anode 199 as another form of heat sink.The electrical fuse element 198 can, for example, be used as theresistive element 31 a illustrated in FIG. 5( a). The electrical fuseelement 198 includes an anode 199, a cathode 190, a body 191, and anactive region 193 near the anode 199. The active region 193 underneaththe anode 199 makes the oxide thinner in the area than the other (i.e.,thin gate oxide instead of thick STI oxide). The thinner oxide above theactive region 193 can dissipate heat faster to create a temperaturegradient to accelerate programming. In other embodiment, the thin oxidearea can be placed underneath the cathode, body, or anode in part or inall of a fuse element as a heat sink in one side, two sides, or anysides.

FIG. 7( a 3 b) shows a top view of an electrical fuse element 198′according to another embodiment. The electrical fuse element 198′ issimilar to the one shown in FIG. 7( a) except thinner oxide regions 193′are placed close to the anode 199′ as another form of heat sink. Theelectrical fuse element 198′ can, for example, be used as the resistiveelement 31 a illustrated in FIG. 5( a). The electrical fuse element 198′includes an anode 199′, a cathode 190′, a body 191′, and an activeregion 193′ near the anode 199′. The active region 193′ close to theanode 199′ of the fuse element 198′ makes the oxide thinner in the areathan the other (i.e., thin gate oxide instead of thick STI oxide) andcan dissipate heat faster to create a temperature gradient to accelerateprogramming. In other embodiment, the thin oxide area can be placed nearto the cathode, body, or anode of a fuse element in one, two, three,four, or any sides to dissipate heat faster. In other embodiment, therecan be at least one substrate contact coupled to an active region, suchas 193′, to prevent latch-up. The contact pillar and/or the metal abovethe substrate contact can also serve as another form of heat sink.

FIG. 7( a 3 c) shows a top view of an electrical fuse element 198″according to yet another embodiment. The electrical fuse element 198″ issimilar to the one shown in FIG. 7( a) except an extended anode region195″ which serves as heat sink. The electrical fuse element 198″ can,for example, be used as the resistive element 31 a illustrated in FIG.5( a). The electrical fuse element 198″ includes an anode 199″, acathode 190″, a body 191″, and an extended anode region 195″. Theextended anode region 195″ can dissipate heat faster than an anode witha single contact area only and without extended region. In oneembodiment, the extended anode area can be only one side, instead of twosides to fit into small cell space, and/or the length can be longer orshorter. In another embodiment, the extended area can be a portion of acathode with one side or two sides. In yet another embodiment, a part orall of the cathode, body, or anode of a fuse element can be made larger,or coupled to a single or plural of conductors (i.e., polysilicon,metal, or active region) near by or in contact as heat sink(s) todissipate heat faster. The extended area means there is no currentflowing through but providing more surfaces or areas to increase thermalconductivity.

FIG. 7( a 3 d) shows a top view of an electrical fuse element 198′″according to yet another embodiment. The electrical fuse element 198′″is similar to the one shown in FIG. 7( a) except a heater 195′″ iscreated near the cathode. The electrical fuse element 198′″ can, forexample, be used as the resistive element 31 a illustrated in FIG. 5(a). The electrical fuse element 198′″ includes an anode 199′″, a cathode190′″, a body 191′″, and high resistance area 195′″ which can serve as aheater. The high resistance area 195′″ can generate more heat to assistprogramming the fuse element. In one embodiment, the heater can be anunsilicided polysilicon or unsilicided active region with a higherresistance than the silicided polysilicon or silicided active region,respectively. In another embodiment, the heater can be a single or aplurality of contact and/or via in serial to contribute more resistanceand generate more heat along the programming path. In yet anotherembodiment, the heater can be a portion of high resistance interconnectto provide more heat to assist programming. The heater 195″″ can beplace to the cathode, anode, or body, in part or all of the fuseelement.

A heat sink can be used to create a temperature gradient to acceleratingprogramming. The heat sink as shown in FIG. 7( a 2), 7(a 3), 7(a 3 a),7(a 3 b), and 7(a 3 c) are for illustrative purposes. A heat sink can bea thin oxide area placed near or underneath the anode, body, or cathodeof a fuse element in one, two, three, four, or any sides to dissipateheat faster. A heat sink can be an extended area of the anode, body, orcathode of a fuse element to increase heat dissipation area withoutcurrent flowing through. A heat sink can also be a single or a pluralityof conductors coupled to (i.e., in contact or in proximity) the anode,body, or cathode of a fuse element to dissipate heat faster. A heat sinkcan also be a large area of anode or cathode with more than one contactto increase heat dissipation area. A heat sink can also be a contactpillar built above an active region near the cathode, body, or anode ofthe fuse element to prevent latch-up and can also dissipate heat faster.In an OTP cell that has a shared contact, i.e., using a metal tointerconnect MOS gate and active region in a single contact, can beconsidered as another kind of heat sink for MOS gate to dissipate heatinto the active region faster. With heat sink, the thermal conduction ofa fuse element can be increased from 20% to 200% in some embodiments.Similarly, a heat generator can be used to create more heat to assistprogramming the fuse element. A heater can usually be a high resistancearea placed to or near the cathode, body, or anode in part or all of thefuse element to generate more heat. A heater can be embodied as a singleor a plurality of unsilicided polysilicon, unsilicided active region, asingle or a plurality of contact, via, or combined in serial, or asingle or a plurality of segment of high resistance interconnect in theprogramming path. The resistance of the heat generator can be from 8Ω to200Ω, or more desirably from 20Ω to 100Ω, in some embodiments. The fuseelement with heat sink or heater can be an interconnect made ofpolysilicon, silicided polysilicon, silicide, polymetal, metal, metalalloy, metal gate, local interconnect, metal-0, thermally isolatedactive region, or CMOS gate, etc. There are many variations and yetequivalent embodiments of heat sinks to dissipate heat and/or heaters toprovide more heat to assist programming and that they are all within thescope of this invention.

FIG. 7( a 4) shows a top view of an electrical fuse element 98′according to another embodiment. The electrical fuse element 98′ issimilar to the one shown in FIG. 7( a) except the fuse element has atleast one notch in the body to assist programming. More generally, atarget portion of the body 91′ can be made formed with less area (e.g.,thinner), such as a notch. The electrical fuse element 98′ can, forexample, be used as the resistive element 31 a illustrated in FIG. 5(a). The electrical fuse element 98′ can include an anode 99′, a cathode90′, and a body 91′. The body 91′ has at least a notch 95′ so that thefuse element can be easily broken during programming. The notch can beembodied as a single or plural of narrow regions in other embodiments.

FIG. 7( a 5) shows a top view of an electrical fuse element 98″according to another embodiment. The electrical fuse element 98″ issimilar to the one shown in FIG. 7( a) except the fuse element is partNMOS and part PMOS metal gates. The electrical fuse element 98″ can, forexample, be used as the resistive element 31 a illustrated in FIG. 5(a). The electrical fuse element 98″ can include an anode 99″, a cathode90″, and bodies 91″ and 93″ fabricated from at least one segment of PMOSand NMOS metal gates, respectively. By using different types of metalsin the same fuse element, the thermal expansion can create a largestress to rupture the fuse when the temperature is raised duringprogramming. The PMOS and NMOS metal gates can be interchangeablebetween the cathode and anode in other embodiments.

FIG. 7( a 6) shows a top view of an OTP element 888 according to anotherembodiment. The OTP element 888 is similar to the one shown in FIG. 7(a) except the OTP element is built with a polysilicon between metalgates. The OTP element 888 can, for example, be used as the resistiveelement 31 a illustrated in FIG. 5( a). The OTP element 888 can includean NMOS metal gate as anode 889, a PMOS metal gate as cathode 891, and apolysilicon as body 881. In a gate-last or Replacement Metal Gate (RMG)process, polysilicon can be provided and used as place holders for CMOSgates. After high temperature cycles of silicidation and source/drainannealing, the polysilicon gates are etched and replaced by metal gates.Different types of metals can be used for NMOS and PMOS metal gates tosuite NMOS/PMOS threshold voltage requirements. Since use of polysiliconas gates or interconnects are available before being replaced by metalgates, a portion of polysilicon can be preserved by modifying the layoutdatabase with layout logic operations. For example, the N+ and P+implant layers with N well can be used to define NMOS and PMOS in theconventional CMOS. The N+ and P+ layers can be modified with mask logicoperations as N′+ layer 835 and P′+ layer 838 so that a segment ofpolysilicon 881 can be preserved. The polysilicon as an OTP body 881 canbe implanted by NLDD, PLDD, N+ source/drain, P+ source/drain, orthreshold voltage adjust implants with minimum masks increment, if any.The polysilicon 881 can be all N, all P, or part N and part P. The OTPelement can be breakdown by high voltage or high current. In oneembodiment, the polysilicon body can be between the same NMOS or PMOSmetal gates. In another embodiment, the polysilicon body is coupled toneither NMOS nor PMOS metal gate.

FIG. 7( a 7) shows a top view of a diode 888′ according to anotherembodiment. The diode 888′ is similar to the OTP element 888 shown inFIG. 7( a 6) except the OTP body is further divided into N type and Ptype regions to act as a diode. The diode 888′ can, for example, be usedas the resistive element 31 a or program selector 31 b illustrated inFIG. 5( a). The diode 888′ includes an NMOS metal gate 889′ and a PMOSmetal gate 891′ as interconnect, and a polysilicon 881′ as body. Thepolysilicon body can be created by blocking at least one portion of NMOSor PMOS metal gate, or both. The polysilicon body 881′ is furtherdivided into three regions 881′-1, 881′-3, and 881′-2, covered bymodified NLDD′ layer 845′, modified PLDD′ layer 848′, and none,respectively. The layers 845′ and 848′ can be generated from NLDD andPLDD layers with mask logic operations so that the areas 881′-1 and881′-3 can receive NLDD and PLDD implants, respectively. The NLDD′ 845′and PLDD′ 848′ can be separated with a space D. The doping concentrationin the space region can be slightly N or P, or unintentionally doped.The width of the space and/or the doping level in the space region canbe used to adjust the diode's breakdown or leakage current. A silicideblock layer (SBL) 885′ can cover the space and overlap into bothregions. The SBL 885′ can be used to block silicide formation to preventthe bodies 881′-1 and 881′-3 from being shorts in one embodiment. Thebodies 881′-1 and 881′-3 are coupled to NMOS metal gate 889′ and PMOSmetal gate 891′, respectively, which serve as the N and P terminals ofthe polysilicon diode. The diode can be used as an OTP element byjunction breakdown under forward or reverse bias, or can be used asprogram selector. The NLDD or PLDD layer in the above discussions is forillustrative purposes. Any layers such as N+, P+, NLDD, PLDD,high-Resistance, or Vt-adjust implants can be used to construct apolysilicoon diode with minimum masks increment. The diode 888′ can beplaced between metal gates of same kind or different kind in differentorder in other embodiments.

FIG. 7( a 8) shows a 3D view of a metal fuse element 910 having two endsA and B, constructed from a contact 911 and a segment of metal-1 912according to one embodiment. The metal fuse element 910 has one end Acoupled to a contact 911, which is coupled to a segment of metal-1 912.The other end of the metal-1 912 is the end B of the metal fuse element910. When a high current flows through the metal fuse element 910, thehigh contact resistance (i.e., 60 ohm in 28 nm CMOS, for example) cangenerate additional Joule heat, to supplement the metal Joule heat, toassist programming the metal-1 912.

FIG. 7( a 9) shows a 3D view of another metal fuse element 920 havingtwo ends A and B, constructed from a contact 921, two vias 923 and 925,and segment(s) of metal-1 and metal-2. The metal fuse element 920 hasone end A coupled to a contact 921, which is further coupled to ametal-2 924 through a metal-1 922 and a via 923. The metal-2 924 iscoupled to another metal-1 926 through another via 925. The other end ofthe metal-1 926 is the end B of the metal fuse element 920. The contact921 and vias 922 and 925 can generate additional heat to assistprogramming the metal-1 926. For example, in an advanced MOStechnologies such as 28 nm, a contact resistance can be 60 ohm and a viaresistance can be 10 ohm. By building up contacts and vias in series,the resistance in the programming path can be increased substantially togenerate more Joule heat for programming metal-1 926, to supplement themetal Joule heating alone.

FIG. 7( a 10) shows a 3D view of yet another metal fuse element 930having two ends A and B, constructed from three contacts, one metalgate, and two segments of metal-1. The metal fuse element 930 has oneend A coupled to a contact 931, which is further coupled to a metal gate934 through a metal-1 932 and another contact 933. The metal gate 934 iscoupled to anther metal-1 936 through another contact 935. The other endof the metal-1 936 is the end B of the metal fuse element 930. There arethree contacts to generate more heat, i.e., 180 ohm if each contact has60 ohm, for programming the metal-1 926, to supplement the metal Jouleheat alone. This embodiment is more suitable when the metal gate isharder to program than the metal-1.

The embodiments in FIGS. 7( a 8), 7(a 9), and 7(a 10) are suitable forthose interconnect fuses that have low resistivity, i.e., metal or somekinds of local interconnect that has sheet resistance of 0.1-0.5 ohm/sq,for example. By building up a plurality of contacts, vias, or combinedin series, more heat can be generated to raise the temperature to assistprogramming. These embodiments can be applied to any kinds of metals,such as metal gate, local interconnect, metal-1, metal-2, etc. Theseembodiments can also be applied to any kind or any number of contacts,via1 (between metal-1 and metal-2), or via2 (between metal-2 andmetal-3), etc. It is more desirable to keep metal to be programmed long(i.e., length/width>20) and the jumpers such as the other metals, metalgate, or local interconnect short (i.e., length/width<5) so that hightemperature can occur in the metal to be programmed. The long metal linecan be serpentine to fit into small area. Using jumpers andcontacts/vias can be more than one set to further increase theresistance and raise the temperature. There can be many variations ofequivalent embodiments in using contacts, vias, or combined to assistprogramming metal fuses. For example, the metal to be programmed can bemetal gate, local interconnect, metal-1, metal-2, metal-3, or metal-4,etc. The via can be any types of via, such as via2 between metal-2 andmetal-3. The number of via or contact can be any, or none. Thedirections of current flow can be downstream or upstream, i.e., currentflows from metal-2 to metal-1 or from metal-1 to metal-2. It is moredesirable for the end A coupled to a diode as program selector with nomore than two contacts, and for the end B coupled to wider metals withmore vias. Those skilled in the art understand that there are manyequivalent embodiments of the metal fuses using heat generated fromcontact or via to assist programming and that are still within the scopeof this invention.

The OTP elements shown in FIGS. 7( a), 7(a 1)-7(a 10) are only toillustrate certain embodiments. As denoted, the OTP elements can bebuilt from any interconnects, including but not limited to polysilicon,silicided polysilicon, silicide, polymetal, local interconnect, metal-0,metal, metal alloy, thermally isolative active region, CMOS gate, orcombinations thereof. The OTP elements can be N type, P type, or part Nand part P type. Each of the OTP elements can have an anode, a cathode,and at least one body. The anode or cathode contacts can be no more than2 for polysilicon/local interconnect/metal-0, and can be no more than 4for metal fuse, preferably. The contact size can be larger than at leastone contact outside of the OTP memory array. The contact enclosure canbe smaller than at least one contact enclosure outside of the OTP memoryarray to lower the electromigration threshold. The length to width ratioin the body can be between 0.5-8 for polysilicon/localinterconnect/metal-0, or 2-6 more desirably, or in the case ofmetal-0/metal even larger than 10, for example. There are manyvariations or combinations of embodiments in part or all that can beconsidered equivalent embodiments.

Polysilicon used to define CMOS gates or as interconnect in ahigh-K/metal-gate CMOS process can also be used as OTP elements. Thefuse element can be P type, N type, or part N and part P type ifapplicable. Particularly, the after/before resistance ratio can beenhanced for those fuse elements that have P+ and N+ implants to createa diode after being programmed, such as polysilicon, thermally isolatedactive region, or gate of a high-K/metal-gate CMOS. For example, if ametal-gate CMOS has a sandwich structure of polysilicon between metalalloy layers, the metal alloy layers may be blocked by masks generatedfrom layout database to create a diode in the fuse elements. In SOI orSOI-like processes, a fuse element can also be constructed from athermally isolated active region such that the fuse element can beimplanted with N+, P+, or part N+ and part P+ in each end of the activeregion. If a fuse element is partly implanted with N+ and P+, the fuseelement can behave like a reverse-biased diode, such as when silicide ontop is depleted after being programmed. In one embodiment, if there isno silicide on top of active regions, an OTP element can also beconstructed from an isolated active region with part N+ and part P+ toact as a diode for breakdown in forward or reverse biased conditions.Using isolated active region to construct an OTP element, the OTPelement can be merged with part of the program-selector diode in onesingle active island to save area.

In some processing technologies that can offer Local Interconnect, localinterconnect can be used as part or all of an OTP element. Localinterconnect, can also be called as metal-0 (M0) in advanced CMOS nodes,has a capability to interconnect polysilicon or MOS gate with an activeregion directly. In advanced MOS technologies beyond 28 nm, the scalingalong the silicon surface dimensions is much faster than scaling in theheight. As a consequence, the aspect ratio of CMOS gate height to thechannel length is very large such that making contacts between metal 1and source/drain or CMOS gate very difficult in terms of device area,performance, and cost. Local interconnect can be used as an intermediateinterconnect between source/drain to CMOS gate, between CMOS gate tometal1, or between source/drain to metal1 in one or two levels The localinterconnects, metal-0, CMOS gate, or combination can be used as an OTPelement in one embodiment. The OTP element and one terminal of theprogram-selector diode can be connected directly through localinterconnect without needing any contacts to save area in anotherembodiment.

Those skilled in the art understand that the above discussions are forillustration purposes and that there are many variations and equivalentsin constructing electrical fuse, anti-fuse elements, or programselectors in CMOS processes,

FIGS. 7( b), 7(c), 7(d), 7(e), 7(f), 7(g) and 7(h) show top views of P+on N well diodes constructed with different embodiments of isolation andfuse elements. Without isolation, P+ and N+ active regions would beshorted together by silicide grown on top. The isolation can be providedby STI, dummy CMOS gate, SBL, or some combination thereof from one tofour (1-4) or any sides or between cells. The P+ and N+ active regionsthat act as P and N terminals of the diodes are sources or drains ofCMOS devices. Both the P+ and N+ active regions reside in an N well,which is the same N well that can be used to house PMOS in standard CMOSprocesses. The N+ active region of the diodes in multiple cells can beshared, though for simplicity FIGS. 7( b)-7(h) show only one N+ activeregion for one P+ active region.

FIG. 7( b) shows a top view of one embodiment of an electrical fuse cell40 including a P+/N well diode having active regions 43 and 44 with STI49 isolation in four sides. A fuse element 42 is coupled to the activeregion 43 through a metal 46. The active regions 43 and 44 are coveredby a P+ implant 47 and N+ implant (the complement of P+ implant 47),respectively, to constitute the P and N terminals of the diode 40. Theactive regions 43 and 44 of the diode 40 reside in an N well 45, thesame N well can be used to house PMOS in standard CMOS processes. Inthis embodiment, the P+ active region 43 and N+ active region 44 aresurrounded by an STI 49 in four (4) sides. Since the STI 49 is muchdeeper than either the N+ or P+ active region, the resistance of thediode 40 between the P+ active region 43 and N+ active region 44 ishigh.

FIG. 7( c) shows a top view of another embodiment of an electrical fusecell 50 including a P+/N well diode having active regions 53 and 54 withan STI 59 isolation in two sides and a dummy MOS gate 58 in another twosides. An active region 51 with two STI slots 59 in the right and leftis divided into a peripheral 54 and a central 53 regions by two MOSgates 58 on top and bottom. The dummy MOS gate 58 is preferably biasedto a fixed voltage. The central active region 53 is covered by a P+implant 57, while the peripheral active region 54 is covered by an N+implant layer (the complement of the P+ implant), which constitute the Pand N terminals of the diode 50. The active region 51 resides in an Nwell 55, the same N well can be used to house PMOS in standard CMOSprocesses. A fuse element 52 is coupled to the P+ active region 53. Inthis embodiment, the P+ active region 53 and N+ active region 54 aresurrounded by STI 59 in left and right sides and the dummy MOS gate 58on top and bottom. The isolation provided by the dummy MOS gate 58 canhave lower resistance than the STI isolation, because the space betweenthe P+ active region 53 and N+ active region 54 may be narrower andthere is no oxide to block the current path underneath the siliconsurface.

FIG. 7( d) shows a top view of yet another embodiment of an electricalfuse cell 60 including a P+/N well diode with dummy MOS gate 68providing isolation in four sides. An active region 61 is divided into acenter active region 63 and a peripheral active region 64 by aring-shape MOS gate 68. The center active region 63 is covered by a P+implant 67 and the peripheral active region 64 is covered by an N+implant (the complement of the P+ implant 67), respectively, toconstitute the P and N terminals of the diode 60. The active region 61resides in an N well, the same N well can be used to house PMOS instandard CMOS processes. A fuse element 62 is coupled to the P+ activeregion 63 through a metal 66. The dummy MOS gate 68, which can be biasedat a fixed voltage, provides isolation between P+ active region 63 andN+ active region 64 regions on four sides. This embodiment offers lowresistance between P and N terminals of the diode 60.

FIG. 7( e) shows a top view of yet another embodiment of an electricalfuse cell 60′ including a P+/N well diode having active regions 63′ and64′ with Silicide Block Layer (SBL) 68′ providing isolation in foursides. An active region 61′ is divided into a center active region 63′and a peripheral active region 64′ by an SBL ring 68′. The center activeregion 63′ and the peripheral active region 64′ are covered by a P+implant 67′ and an N+ implant (the complement of P+ implant 67′),respectively, to constitute the P and N terminals of the diode 60′. Theboundaries between the P+ implant 67′ and N+ implants are about in themiddle of the SBL ring 68′. The active region 61′ resides in an N well65′. A fuse element 62′ is coupled to the P+ active region 63′ through ametal 66′. The SBL ring 68′ blocks silicide formation on the top of theactive regions between P+ active region 63′ and N+ active region 64′. Inthis embodiment, the P+ active region 63′ and N+ active region 64′ areisolated in four sides by P/N junctions. This embodiment has lowresistance between the P and N terminals of the diode 60′, though theSBL may be wider than a MOS gate. In another embodiment, there is aspace between the P+ implant 67′ and the N+ implant that is covered bythe SBL ring 68′.

FIG. 7( f) shows a top view of another embodiment of an electrical fusecell 70 having a P+/N well diode with an abutted contact. Active regions73 and 74, which are isolated by an STI 79, are covered by a P+ implant77 and an N+ implant (the complement of the P+ implant 77),respectively, to constitute the P and N terminals of the diode 70. Bothof the active regions 73 and 74 reside in an N well 75, the same N wellcan be used to house PMOS in standard CMOS processes. A fuse element 72is coupled to the P+ active region 73 through a metal 76 in a singlecontact 71. This contact 71 is quite different from the contacts inFIGS. 7( b), (c), (d), and (e) where a contact can be used to connect afuse element with a metal and then another contact is used to connectthe metal with a P+ active region. By connecting a fuse element directlyto an active region through a metal in a single contact, the cell areacan be reduced substantially. The abutted contact can be larger than aregular contact and, more particularly, can be a large rectangularcontact that has about twice the area of a regular contact in a CMOSprocess. This embodiment for a fuse element can be constructed by a CMOSgate, including polysilicon, silicided polysilicon, or non-aluminummetal CMOS gate, that allows an abutted contact.

FIG. 7( g) shows a top view of yet another embodiment of fuse cells 70′with a central cell 79′ and a portion of left/right cells. The centralcell 79′ includes an electrical fuse element 72′ and a diode as programselector. An active region 71′ is divided into upper active regions 73′,73″, and 73′″ and a lower active region 74′ by a U-shape dummy MOS gate78′. The upper active regions 73′, 73″, and 73′″ are covered by a P+implant 77′ while the rest of lower active region 74′ is covered by anN+ implant (the complement of the P+ implant 77′). The active region 73′and 74′ constitute the P and N terminals of the diode in the centralcell 79′. The active region 73″ serves as a P terminal of a diode in theleft cell, while the active region 73′″ serves as a P terminal of adiode in the right cell. The polysilicon 78′ isolates the P+/N+ of thediode in the central cell 79′ and also isolates the P+ terminals of theleft, central, and right cells by tying the polysilicon 78′ to a highvoltage (i.e., V+ in FIG. 5( a)). The polysilicon 78′ can be a dummy MOSgate fabricated in standard CMOS processes. The active region 71′resides in an N well, the same N well that can be used to house PMOS instandard CMOS processes. A fuse element 72′ is coupled to the P+ activeregion 73′ through a metal 76′ in the central cell 79′. This embodimentcan offer low resistance between P and N terminals of the diode in thecentral cell 79′ while providing isolations between the cells in theleft and right.

FIG. 7( h) shows a top view of yet another embodiment of a fuse cell 70″that has a dummy MOS gate 78″ providing isolation between P+/N+ in Nwell as two terminals of a diode and an electrical fuse element 72″. Anactive region 71″ is divided into an upper active regions 73″ and alower active region 74″ by a dummy MOS gate 78″. The upper active region73″ can be covered by a P+ implant 77″ while the lower active region 74″can be covered by an N+ implant (the complement of the P+ implant 77″).The active regions 73″ and 74″ constitute the P and N terminals of thediode in the cell 70″. The polysilicon 78″ provides isolation betweenthe P+/N+ of the diode in the cell 70″ and can be tied to a fixed bias.The polysilicon 78″ is a dummy MOS gate fabricated in standard CMOSprocesses and can be a metal gate in advanced metal-gate CMOS processes.The width of the dummy MOS gate can be close to the minimum gate widthof a CMOS technology. The active region 71″ resides in an N well 75″,the same N well that can be used to house PMOS in standard CMOSprocesses. A fuse element 72″ can be coupled to the P+ active region 73″through a metal 76″ in one end (through contacts 75″-2 and 75″-3) and toa high voltage supply line V+ in the other end (through contact 75″-1).The N+ region 74″ is coupled to another voltage supply line V− throughanother contact 75″-4. At least one of the contacts 75″-1, 2, 3, 4 canbe larger than at least one contacts outside of the memory array toreduce the contact resistance in one embodiment. When high and lowvoltages are applied to V+ and V−, respectively, a high current can flowthrough the fuse element 72″ to program the fuse element 72″ into a highresistance state accordingly.

In general, a polysilicon or silicide polysilicon fuse is more commonlyused as an electrical fuse because of its lower program current thanmetal or contact/via fuses. However, a metal fuse has some advantagessuch as smaller size and wide resistance ratio after being programmed.Metal as a fuse element allows making contacts directly to a P+ activeregion thus eliminating one additional contact as compared to using apolysilicon fuse. In advanced CMOS technologies with feature size lessthan 40 nm, the program voltage for metal fuses can be lower than 3.3V,which makes metal fuse a viable solution.

FIG. 8( a) shows a top view of a metal1 fuse cell 60″ including a P+/Nwell diode 60″ with dummy CMOS gate isolation. An active region 61 isdivided into a center active region 63 and a peripheral active region 64by a ring-shape MOS gate 68. The center active region 63 is covered by aP+ implant 67 and the peripheral active region 64 is covered by an N+implant (the complement of the P+ implant 67), respectively, toconstitute the P and N terminals of a diode. The active region 61resides in an N well 65, the same N well can be used to house PMOS instandard CMOS processes. A metal1 fuse element 62″ is coupled to the P+region 63 directly. The ring-shape MOS gate 68, which provides dummyCMOS gate isolation, can be biased at a fixed voltage, and can provideisolation between P+ active 63 and N+ active 64 regions in four sides.In one embodiment, the length to width ratio of a metal fuse can beabout or larger than 10 to 1 to lower the electromigration threshold.

The size of the metal fuse cell in FIG. 8( a) can be further reduced, ifthe turn-on resistance of the diode is not crucial. FIG. 8( b) shows atop view of a row of metal fuse cells 60′″ having four metal fuse cellsthat share one N well contact in each side in accordance with oneembodiment. Metal1 fuse 69 has an anode 62′, a metal1 body 66′, and acathode coupled to an active region 64′ covered by a P+ implant 67′ thatacts as the P terminal of a diode. The active region 61′ resides in an Nwell 65′. Another active region 63′ covered by an N+ implant (complementof P+ implant 67′) acts as N terminal of the diode. Four diodes areisolated by STI 68′ and share one N+ active region 63′ each side. The N+active regions 63′ are connected by a metal2 running horizontally, andthe anode of the diode is connected by a metal3 running vertically. Ifmetal1 is intended to be programmed, other types of metals in theconduction path should be wider. Similarly, more contacts and viasshould be put in the conduction path to resist undesirable programming.Using metal1 as a metal fuse in FIG. 8( b) is for illustrative purposes,those skilled in the art understand that the above description can beapplied to any metals, such as metal0, metal2, metal3, or metal4 inother embodiments. Similarly, those skilled in the art understand thatthe isolation, metal scheme, and the number of cells sharing one N+active may vary in other embodiments.

Contact or via fuses may become more viable for advanced CMOStechnologies with feature size less than 65 nm, because smallcontact/via size makes program current rather low. FIG. 8( c) shows atop view of a row of four via1 fuse cells 70 sharing N type wellcontacts 73 a and 73 b in accordance with one embodiment. Vial fuse cell79 has a via1 79 a coupled to a metal1 76 and a metal2 72. Metal2 72 iscoupled to a metal3 through via2 89 running vertically as a bitline.Metal1 76 is coupled to an active region 74 covered by a P+ implant 77that acts as the P terminal of a diode 71. Active regions 73 a and 73 bcovered by an N+ implant (complement of P+ implant 77) serves as the Nterminal of the diode 71 in via1 fuse cell 79. Moreover, the activeregions 73 a and 73 b serve as the common N terminal of the diodes inthe four-fuse cell 70. They are further coupled to a metal4 runninghorizontally as a wordline. The active regions 74, 73 a, and 73 b residein the same N well 75. Four diodes in via1 fuse cells 70 have STI 78isolation between each other. If via1 is intended to be programmed, morecontacts and more other kinds of vias should be put in the conductionpath. And metals in the conduction path should be wider and containlarge contact/via enclosures to resist undesirable programming. Vial asa via fuse in FIG. 8( c) is for illustrative purpose, those skilled inthe art understand that the above description can be applied to anykinds of contacts or vias, such as via2, via3, or via4, etc. Similarly,those skilled in the art understand that the isolation, metal scheme,and the number of cells sharing one N+ active may vary in otherembodiments.

FIG. 8( d) shows a top view of an array of 4×5 via1 fuses 90 with dummyCMOS gate isolation in accordance with one embodiment. The one-row viafuse shown in FIG. 8( c) can be extended into a two-dimensional array 90as shown in FIG. 8( d). The array 90 has four rows of active regions 91,each residing in a separate N well, and five columns of via fuse cells96, isolated by dummy CMOS gates 92 between active regions. Each viafuse cell 96 has one contact 99 on an active region covered by a P+implant 94 that acts as the P terminal of a diode, which is furthercoupled to a metal2 bitline running vertically. Active regions in twosides of the array 90 are covered by N+ implant 97 to serve as the Nterminals of the diodes in the same row, which is further coupled tometal3 as wordlines running horizontally. To program a via fuse, selectand apply voltages to the desired wordline and bitline to conduct acurrent from metal2 bitline, via1, metal1, contact, P+ active, N+active, to metal3 wordline. To ensure only via1 is programmed, metalscan be made wider and the numbers of other types of vias or contact canbe more than one. To simplify the drawing, metal1-via1-metal2 connectioncan be referred to FIG. 8( c) and, therefore, is not shown in each cellin FIG. 8( d). Those skilled in the art understand that various types ofcontact or vias can be used as resistive elements and the metal schemesmay change in other embodiments. Similarly, the number of cells in rowsand columns, the numbers of rows or columns in an array, and the numbersof cells between N+ active may vary in other embodiments.

FIG. 9( a) shows a cross section of a programmable resistive device cell40 using phase-change material as a resistive element 42, with buffermetals 41 and 43, and a P+/N well diode 32, according to one embodiment.The P+/N well diode 32 has a P+ active region 33 and N+ active region 37on an N well 34 as P and N terminals. The isolation between the P+active region 33 and N+ active region 37 is an STI 36. The P+ activeregion 33 of the diode 32 is coupled to a lower metal 41 as a bufferlayer through a contact plug 40-1. The lower metal 41 is then coupled toa thin film of phase change material 42 (e.g., GST film such asGe2Sb2Te5 or AgInSbTe, etc.) through a contact plug 40-2. An upper metal43 also couples to the thin film of the phase-change material 42. Theupper metal 43 is coupled to another metal 44 to act as a bitline (BL)through a plug 40-3. The phase-change film 42 can have a chemicalcomposition of Germanimum (Ge), Antimony (Sb), and Tellurium (Te), suchas Ge_(x)Sb_(y)Te_(z) (x, y and z are any arbitrary numbers), or as oneexample Ge₂Sb₂Te₅ (GST-225). The GST film can be doped with at least oneor more of Indium (In), Tin (Sn), or Selenium (Se) to enhanceperformance. The phase-change cell structure can be substantiallyplanar, which means the phase-change film 42 has an area that is largerthan the film contact area coupled to the program selector, or theheight from the surface of the silicon substrate to the phase-changefilm 42 is much smaller than the dimensions of the film parallel tosilicon substrate. In this embodiment, the active area of phase-changefilm 42 is much larger than the contact area so that the programmingcharacteristics can be more uniform and reproducible. The phase-changefilm 42 is not a vertical structure and does not sit on top of a tallcontact, which can be more suitable for embedded phase-change memoryapplications, especially when the diode 32 (i.e., junction diode) isused as program selector to make the cell size very small. For thoseskilled in the art understand that the structure and fabricationprocesses may vary and that the structures of phase-change film (e.g.,GST film) and buffer metals described above are for illustrativepurpose.

FIG. 9( b) shows a top view of a PCM cell using a junction diode asprogram selector having a cell boundary 80 in accordance with oneembodiment. The PCM cell has a P+/N well diode and a phase-changematerial 85, which can be a GST film. The P+/N well diode has activeregions 83 and 81 covered by a P+ implant 86 and an N+ implant(complement of P+ implant 86), respectively, to serve as the anode andcathode. Both active regions 81 and 83 reside on an N well 84, the sameN well can be used to house PMOS in standard CMOS processes. The anodeis coupled to the phase-change material 85 through a metal1 82. Thephase-change material 85 is further coupled to a metal3 bitline (BL) 88running vertically. The cathode of the P+/N well diode (i.e., activeregion 81) is connected by a metal2 wordline (WL) 87 runninghorizontally. By applying a proper voltage between the bitline 88 andthe wordline 87 for a suitable duration, the phase-change material 85can be programmed into a 0 or 1 state accordingly. Since programming thePCM cell is based on raising the temperature rather thanelectro-migration as with an electrical fuse, the phase-change film(e.g., GST film) can be symmetrical in area for both anode and cathode.Those skilled in the art understand that the phase-change film,structure, layout style, and metal schemes may vary in otherembodiments.

Programming a phase-change memory (PCM), such as a phase-change film,depends on the physical properties of the phase-change film, such asglass transition and melting temperatures. To reset, the phase-changefilm needs to be heated up beyond the melting temperature and thenquenched. To set, the phase-change film needs to be heated up betweenmelting and glass transition temperatures and then annealed. A typicalPCM film has glass transition temperature of about 200° C. and meltingtemperature of about 600° C. These temperatures determine the operationtemperature of a PCM memory because the resistance state may changeafter staying in a particular temperature for a long time. However, mostapplications require retaining data for 10 years for the operationtemperature from 0 to 85° C. or even from −40 to 125° C. To maintaincell stability over the device's lifetime and over such a widetemperature range, periodic reading and then writing back data into thesame cells can be performed. The refresh period can be quite long, suchas longer than a second (e.g., minutes, hours, days, weeks, or evenmonths). The refresh mechanism can be generated inside the memory ortriggered from outside the memory. The long refresh period to maintaincell stability can also be applied to other emerging memories such asRRAM, CBRAM, and MRAM, etc.

FIG. 10 shows one embodiment of an MRAM cell 310 using diodes 317 and318 as program selectors in accordance with one embodiment. The MRAMcell 310 in FIG. 10 is a three-terminal MRAM cell. The MRAM cell 310 hasan MTJ 311, including a free layer stack 312, a fixed layer stack 313,and a dielectric film in between, and the two diodes 317 and 318. Thefree layer stack 312 is coupled to a supply voltage V, and coupled tothe fixed layer stack 313 through a metal oxide such as Al₂O₃ or MgO.The diode 317 has the N terminal coupled to the fixed layer stack 313and the P terminal coupled to V+ for programming a 1. The diode 318 hasthe P terminal coupled to the fixed layer stack 313 and the N terminalcoupled to V− for programming a 0. If V+ voltage is higher than V, acurrent flows from V+ to V to program the MTJ 311 into state 1.Similarly, if V− voltage is lower than V, a current flows from V to V−to program the MTJ 311 into state 0. During programming, the other diodeis supposedly cutoff. For reading, V+ and V− can be both set to 0V andthe resistance between node V and V+/V− can be sensed to determinewhether the MTJ 311 is in state 0 or 1.

FIG. 11( a) shows a cross section of one embodiment of an MRAM cell 310with MTJ 311 and junction diodes 317 and 318 as program selectors inaccordance with one embodiment. MTJ 311 has a free layer stack 312 ontop and a fixed layer stack 313 underneath with a dielectric in betweento constitute a magnetic tunneling junction. Diode 317 is used toprogram 1 and diode 318 is used to program 0. Diodes 317 and 318 have P+and N+ active regions on N wells 321 and 320, respectively, the same Nwells to house PMOS in standard CMOS processes. Diode 317 has a P+active region 315 and N+ active region 314 to constitute the P and Nterminals of the program-1 diode 317. Similarly, diode 318 has a P+active 316 and N+ active 319 to constitute the P and N terminals of theprogram-0 diode 318. FIG. 11( a) shows STI 330 isolation for the P and Nterminals of diodes 317 and 318. For those skilled in the art understandthat different isolation schemes, such as dummy MOS gate or SBL, canalternatively be applied.

The free stacks 312 of the MTJ 311 can be coupled to a supply voltage V,while the N terminal of the diode 318 can be coupled to a supply voltageV− and the P terminal of the diode 317 can be coupled to another supplyvoltage V+. Programming a 1 in FIG. 11( a) can be achieved by applying ahigh voltage, i.e., 2V to V+ and V−, while keeping V at ground, or 0V.To program a 1, a current flows from diode 317 through the MTJ 311 whilethe diode 318 is cutoff. Similarly, programming a 0 can be achieved byapplying a high voltage to V, i.e., 2V, and keeping V+ and V− at ground.In this case. a current flows from MTJ 311 through diode 318 while thediode 317 is cutoff.

FIG. 11( b) shows a cross section of another embodiment of an MRAM cell310′ with MTJ 311′ and junction diodes 317′ and 318′ as programselectors in accordance with one embodiment. MTJ 311′ has a free layerstack 312′ on top and a fixed layer stack 313′ underneath with adielectric in between to constitute a magnetic tunneling junction. Diode317′ is used to program 1 and diode 318′ is used to program 0. Diodes317′ and 318′ have P+ and N+ active regions on N wells 321′ and 320′,respectively, which are fabricated by shallow N wells with additionalprocess steps. Though more process steps are needed, the cell size canbe smaller. Diode 317′ has P+ active region 315′ and N+ active region314′ to constitute the P and N terminals of the program-1 diode 317′.Similarly, diode 318′ has P+ active 316′ and N+ active 319′ toconstitute the P and N terminals of the program-0 diode 318′. STI 330′isolates different active regions.

The free stacks 312′ of the MTJ 311′ can be coupled to a supply voltageV, while the N terminal of the diode 318′ can be coupled to a supplyvoltage V− and the P terminal of the diode 317′ is coupled to anothersupply voltage V+. Programming a 1 in FIG. 11( b) can be achieved byapplying a high voltage, i.e., 2V to V+ and V−, while keeping V atground, or 0V. To program a 1, a current will flow from diode 317′through the MTJ 311′ while the diode 318′ is cutoff. Similarly,programming 0 can be achieved by applying a high voltage to V, i.e., 2V,and keeping V+ and V− at ground. In this case, a current will flow fromMTJ 311′ through diode 318′ while the diode 317′ is cutoff.

FIG. 12( a) shows one embodiment of a three-terminal 2×2 MRAM cell arrayusing junction diodes 317 and 318 as program selectors and the conditionto program 1 in a cell in accordance with one embodiment. Cells 310-00,310-01, 310-10, and 310-11 are organized as a two-dimensional array. Thecell 310-00 has a MTJ 311-00, a program-1 diode 317-00, and a program-0diode 318-00. The MTJ 311-00 is coupled to a supply voltage V at oneend, to the N terminal of the program-1 diode 317-00 and to the Pterminal of the program-0 diode 318-00 at the other end. The P terminalof the program-1 diode 317-00 is coupled to a supply voltage V+. The Nterminal of the program-0 diode 318-00 is coupled to another supplyvoltage V−. The other cells 310-01, 310-10, and 310-11 are similarlycoupled. The voltage Vs of the cells 310-00 and 310-10 in the samecolumns are connected to BL0. The voltage Vs of the cells 310-01 and310-11 in the same column are connected to BL1. The voltages V+ and V−of the cells 310-00 and 310-01 in the same row are connected to WL0P andWL0N, respectively. The voltages V+ and V− of the cells 310-10 and310-11 in the same row are connected to WL1P and WL1N, respectively. Toprogram a 1 into the cell 310-01, WL0P is set high and BL1 is set low,while setting the other BL and WLs at proper voltages as shown in FIG.12( a) to disable the other program-1 and program-0 diodes. The boldline in FIG. 12( a) shows the direction of current flow.

FIG. 12( b) shows alternative program-1 conditions for the cell 310-01in a 2×2 MRAM array in accordance with one embodiment. For example, toprogram a 1 into cell 310-01, set BL1 and WL0P to low and high,respectively. If BL0 is set to high in condition 1, the WL0N and WL1Ncan be either high or floating, and WL1P can be either low or floating.The high and low voltages of an MRAM in today's technologies are about2-3V for high voltage and 0 for low voltage, respectively. If BL0 isfloating in condition 2, WL0N and WL1N can be high, low, or floating,and WL1P can be either low or floating. In a practical implementation,the floating nodes are usually coupled to very weak devices to a fixedvoltage to prevent leakage. One embodiment of the program-1 condition isshown in FIG. 12( a) without any nodes floating.

FIG. 13( a) shows one embodiment of a three-terminal 2×2 MRAM cell arraywith MTJ 311 and junction diodes 317 and 318 as program selectors andthe condition to program 0 in a cell in accordance with one embodiment.The cells 310-00, 310-01, 310-10, and 310-11 are organized as atwo-dimensional array. The cell 310-00 has a MTJ 311-00, a program-1diode 317-00, and a program-0 diode 318-00. The MTJ 311-00 is coupled toa supply voltage V at one end, to the N terminal of program-1 diode317-00 and to the P terminal of program-0 diode 318-00 at the other end.The P terminal of the program-1 diode 317-00 is coupled to a supplyvoltage V+. The N terminal of the program-0 diode 318-00 is coupled toanother supply voltage V−. The other cells 310-01, 310-10, and 310-11are similarly coupled. The voltage Vs of the cells 310-00 and 310-10 inthe same columns are connected to BL0. The voltage Vs of the cells310-01 and 310-11 in the same column are connected to BL1. The voltagesV+ and V− of the cells 310-00 and 310-01 in the same row are connectedto WL0P and WL0N, respectively. The voltages V+ and V− of the cells310-10 and 310-11 in the same row are connected to WL1P and WL1N,respectively. To program a 0 into the cell 310-01, WL0N is set low andBL1 is set high, while setting the other BL and WLs at proper voltagesas shown in FIG. 13( a) to disable the other program-1 and program-0diodes. The bold line in FIG. 13( a) shows the direction of currentflow.

FIG. 13( b) shows alternative program-0 conditions for the cell 310-01in a 2×2 MRAM array in accordance with one embodiment. For example, toprogram a 0 into cell 310-01, set BL1 and WL0N to high and low,respectively. If BL0 is set to low in condition 1, the WL0P and WL1P canbe either low or floating, and WL1N can be either high or floating. Thehigh and low voltages of an MRAM in today's technologies are about 2-3Vfor high voltage and 0 for low voltage, respectively. If BL0 is floatingin condition 2, WL0P and WL1P can be high, low, or floating, and WL1Ncan be either high or floating. In a practical implementation, thefloating nodes are usually coupled to very weak devices to a fixedvoltage to prevent leakage. One embodiment of the program-0 condition isas shown in FIG. 13( a) without any nodes floating.

The cells in 2×2 MRAM arrays in FIGS. 12( a), 12(b), 13(a) and 13(b) arethree-terminal cells, namely, cells with V, V+, and V− nodes. However,if the program voltage VDDP is less than twice a diode's thresholdvoltage Vd, i.e., VDDP<2*Vd, the V+ and V− nodes of the same cell can beconnected together as a two-terminal cell. Since Vd is about 0.6-0.7V atroom temperature, this two-terminal cell works if the program highvoltage is less than 1.2V and low voltage is 0V. This is a commonvoltage configuration of MRAM arrays for advanced CMOS technologies thathas supply voltage of about 1.0V. FIGS. 14( a) and 14(b) show schematicsfor programming a 1 and 0, respectively, in a two-terminal 2×2 MRAMarray.

FIGS. 14( a) and 14(b) show one embodiment of programming 1 and 0,respectively, in a two-terminal 2×2 MRAM cell array in accordance withone embodiment. The cells 310-00, 310-01, 310-10, and 310-11 areorganized in a two-dimensional array. The cell 310-00 has the MTJ311-00, the program-1 diode 317-00, and the program-0 diode 318-00. TheMTJ 311-00 is coupled to a supply voltage V at one end, to the Nterminal of program-1 diode 317-00 and the P terminal of program-0 diode318-00 at the other end. The P terminal of the program-1 diode 317-00 iscoupled to a supply voltage V+. The N terminal of the program-0 diode318-00 is coupled to another supply voltage V−. The voltages V+ and V−are connected together in the cell level if VDDP<2*Vd can be met. Theother cells 310-01, 310-10 and 310-11 are similarly coupled. Thevoltages Vs of the cells 310-00 and 310-10 in the same columns areconnected to BL0. The voltage Vs of the cells 310-01 and 310-11 in thesame column are connected to BL1. The voltages V+ and V− of the cells310-00 and 310-01 in the same row are connected to WL0. The voltages V+and V− of the cells 310-10 and 310-11 in the same row are connected toWL1.

To program a 1 into the cell 310-01, WL0 is set high and BL1 is set low,while setting the other BL and WLs at proper voltages as shown in FIG.14( a) to disable other program-1 and program-0 diodes. The bold line inFIG. 14( a) shows the direction of current flow. To program a 0 into thecell 310-01, WL0 is set low and BL1 is set high, while setting the otherBL and WLs at proper voltages as shown in FIG. 14( b) to disable theother program-1 and program-0 diodes. The bold line in FIG. 14( b) showsthe direction of current flow.

The embodiments of constructing MRAM cells in a 2×2 array as shown inFIGS. 12( a)-14(b) are for illustrative purposes. Those skilled in theart understand that the number of cells, rows, or columns in a memorycan be constructed arbitrarily and rows and columns are interchangeable.

The programmable resistive devices can be used to construct a memory inaccordance with one embodiment. FIG. 15 shows a portion of aprogrammable resistive memory 100 constructed by an array 101 of n-rowby (m+1)-column single-diode-as-program-selector cells 110 and nwordline drivers 150-i, where i=0, 1, . . . , n−1, in accordance withone embodiment. The memory array 101 has m normal columns and onereference column for one shared sense amplifier 140 for differentialsensing. Each of the memory cells 110 has a resistive element 111coupled to the P terminal of a diode 112 as program selector and to abitline BLj 170-j (j=0, 1, . . . m−1) or reference bitline BLR0 175-0for those of the memory cells 110 in the same column. The N terminal ofthe diode 112 is coupled to a wordline WLBi 152-i through a localwordline LWLBi 154-i, where i=0, 1, . . . , n−1, for those of the memorycells 110 in the same row. Each wordline WLBi is coupled to at least onelocal wordline LWLBi, where i=0, 1, . . . , n−1. The LWLBi 154-i isgenerally constructed by a high resistivity material, such as N well,polysilicon, local interconnect, metal-0, active region, or metal gateto connect cells, and then coupled to the WLBi (e.g., a low-resistivitymetal WLBi) through conductive contacts or vias, buffers, orpost-decoders 172-i, where i=0, 1, . . . , n−1. Buffers or post-decoders172-i may be needed when using diodes as program selectors because thereare currents flowing through the WLBi, especially when one WLBi drivesmultiple cells for program or read simultaneously in other embodiments.The wordline WLBi is driven by the wordline driver 150-i with a supplyvoltage vddi that can be switched between different voltages for programand read. Each BLj 170-j or BLR0 175-0 is coupled to a supply voltageVDDP through a Y-write pass gate 120-j or 125 for programming, whereeach BLj 170-j or BLR0 175-0 is selected by YSWBj (j=0, 1, . . . , m−1)or YSWRB0, respectively. The Y-write pass gate 120-j (j=0, 1, . . . ,m−1) or 125 can be built by PMOS, though NMOS, diode, or bipolar devicescan be employed in some embodiments. Each BLj or BLR0 is coupled to adataline DLj or DLR0 through a Y-read pass gate 130-j or 135 selected byYSRj (j=0, 1, . . . , m−1) or YSRR0, respectively. In this portion ofmemory array 101, m normal datalines DLj (j=0, 1, . . . , m−1) areconnected to an input 160 of a sense amplifier 140. The referencedataline DLR0 provides another input 161 for the sense amplifier 140 (nomultiplex is generally needed in the reference branch). The output ofthe sense amplifiers 140 is Q0.

To program a cell, the specific WLBi and YSWBj are turned on and a highvoltage is supplied to VDDP, where i=0, 1, . . . n−1 and j=0, 1, . . . ,m−1. In some embodiments, the reference cells can be programmed to 0 or1 by turning on WLRBi, and YSWRB0, where i=0, 1, . . . , n−1. To read acell, a data column 160 can be selected by turning on the specific WLBiand YSRj, where i=0, 1, . . . , n−1, and j=0, 1, . . . , m−1, and areference cell coupled to the reference dataline DLR0 161 can beselected for the sense amplifier 140 to sense and compare the resistancedifference between normal/reference BLs and ground, while disabling allYSWBj and YSWRB0 where j=0, 1, . . . , m−1.

The programmable resistive devices can be used to construct a memory inaccordance with one embodiment. FIG. 16( a) shows a portion of aprogrammable resistive memory 100 constructed by an array 101 of3-terminal MRAM cells 110 in n rows and m+1 columns and n pairs ofwordline drivers 150-i and 151-i, where i=0, 1, . . . , n−1, accordingto one embodiment. The memory array 101 has m normal columns and onereference column for one shared sense amplifier 140 for differentialsensing. Each of the memory cells 110 has a resistive element 111coupled to the P terminal of a program-0 diode 112 and N terminal of aprogram-1 diode 113. The program-0 diode 112 and the program-1 diode 113serve as program selectors. Each resistive element 111 is also coupledto a bitline BLj 170-j (j=0, 1, . . . m−1) or reference bitline BLR0175-0 for those of the memory cells 110 in the same column. The Nterminal of the diode 112 is coupled to a wordline WLNi 152-i through alocal wordline LWLNi 154-i, where i=0, 1, . . . , n−1, for those of thememory cells 110 in the same row. The P terminal of the diode 113 iscoupled to a wordline WLPi 153-i through a local wordline LWLPi 155-i,where i=0, 1, . . . , n−1, for those cells in the same row. Eachwordline WLNi or WLPi is coupled to at least one local wordline LWLNi orLWLPi, respectively, where i=0, 1, . . . , n−1. The LWLNi 154-i andLWLPi 155-i are generally constructed by a high resistivity material,such as N well, polysilicon, local interconnect, metal-0, active region,or metal gate to connect cells, and then coupled to the WLNi or WLPi(e.g., low-resistivity metal WLNi or WLPi) through conductive contactsor vias, buffers, or post-decoders 172-i or 173-i respectively, wherei=0, 1, . . . , n−1. Buffers or post-decoders 172-i or 173-i may beneeded when using diodes as program selectors because there are currentsflowing through WLNi or WLPi, especially when one WLNi or WLPi driversmultiple cells for program or read simultaneously in some embodiments.The wordlines WLNi and WLPi are driven by wordline drivers 150-i and151-i, respectively, with a supply voltage vddi that can be switchedbetween different voltages for program and read. Each BLj 170-j or BLR0175-0 is coupled to a supply voltage VDDP through a Y-write-0 pass gate120-j or 125 to program 0, where each BLj 170-j or BLR0 175-0 isselected by YSOWBj (j=0, 1, . . . , m−1) or YS0WRB0, respectively.Y-write-0 pass gate 120-j or 125 can be built by PMOS, though NMOS,diode, or bipolar devices can be employed in other embodiments.Similarly, each BLj 170-j or BLR0 175-0 is coupled to a supply voltage0V through a Y-write-1 pass gate 121-j or 126 to program 1, where eachBLj 170-j or BLR0 175-0 is selected by YS1Wj (j=0, 1, . . . , m−1) orYS1WR0, respectively. Y-write-1 pass gate 121-j or 126 is can be builtby NMOS, though PMOS, diode, or bipolar devices can be employed in otherembodiments. Each BLj or BLR0 is coupled to a dataline DLj or DLR0through a Y-read pass gate 130-j or 135 selected by YSRj (j=0, 1, . . ., m−1) or YSRR0, respectively. In this portion of memory array 101, mnormal datalines DLj (j=0, 1, . . . , m−1) are connected to an input 160of a sense amplifier 140. Reference dataline DLR0 provides another input161 for the sense amplifier 140, except that no multiplex is generallyneeded in a reference branch. The output of the sense amplifier 140 isQ0.

To program a 0 into a cell, the specific WLNi, WLPi and BLj are selectedas shown in FIG. 13( a) or 13(b) by wordline drivers 150-i, 151-i, andY-pass gate 120-j by YSOWBj, respectively, where i=0, 1, . . . n−1 andj=0, 1, . . . , m−1, while the other wordlines and bitlines are alsoproperly set. A high voltage is applied to VDDP. In some embodiments,the reference cells can be programmed into 0 by setting proper voltagesto WLRNi 158-i, WLRPi 159-i and YS0WRB0, where i=0, 1, . . . , n−1. Toprogram a 1 to a cell, the specific WLNi, WLPi and BLj are selected asshown in FIG. 12( a) or 12(b) by wordline driver 150-i, 151-i, andY-pass gate 121-j by YS1Wj, respectively, where i=0, 1, . . . n−1 andj=0, 1, . . . , m−1, while the other wordlines and bitlines are alsoproperly set. In some embodiments, the reference cells can be programmedto 1 by setting proper voltages to WLRNi 158-i, WLRPi 159-i and YS1WR0,where i=0, 1, . . . , n−1. To read a cell, a data column 160 can beselected by turning on the specific WLNi, WLPi and YSRj, where i=0, 1, .. . , n−1, and j=0, 1, . . . , m−1, and a reference cell coupled to thereference dataline DLR 161 for the sense amplifier 140 to sense andcompare the resistance difference between normal/reference BLs andground, while disabling all YSOWBj, YS0WRB0, YS1Wj and YS1WR0, wherej=0, 1, . . . , m−1.

Another embodiment of constructing an MRAM memory with 2-terminal MRAMcells is shown in FIG. 16( b), provided the voltage difference VDDP,between high and low states, is less than twice of the diode's thresholdvoltage Vd, i.e., VDDP<2*Vd. As shown in FIG. 16( b), two wordlines perrow WLNi 152-i and WLPi 153-i in FIG. 16( a) can be merged into onewordline driver WLNi 152-i, where i=0, 1, . . . , n−1. Also, the localwordlines LWLNi 154-i and LWLP 155-i per row in FIG. 16( a) can bemerged into one local wordline LWLNi 154-i, where i=0, 1, . . . , n−1,as shown in FIG. 16( b). Still further, two wordline drivers 150-i and151-i in FIG. 16( a) can be merged into one, i.e., wordline driver150-i. The BLs and WLNs of the unselected cells are applied with properprogram 1 and 0 conditions as shown in FIGS. 14( a) and 14(b),respectively. Since half of wordlines, local wordlines, and wordlinedrivers can be eliminated in this embodiment, cell and macro areas canbe reduced substantially.

Differential sensing is a common for programmable resistive memory,though single-end sensing can be used in other embodiments. FIGS. 17(a), 17(b), and 17(c) show three other embodiments of constructingreference cells for differential sensing. In FIG. 17( a), a portion ofmemory 400 has a normal array 180 of n×m cells, two reference columns150-0 and 150-1 of n×1 cells each storing all data 0 and 1 respectively,m+1 Y-read pass gates 130, and a sense amplifier 140. As an example, n=8and m=8 are used to illustrate the concept. There are n wordlines WLBiand n reference wordlines WLRBi for each column, where i=0, 1, . . . ,n−1. When a wordline WLBi is turned on to access a row, a correspondingreference wordline WLRBi (i=0, 1, . . . , n−1) is also turned on toactivate two reference cells 170-0 and 170-1 in the same row to providemid-level resistance after proper scaling in the sense amplifier. Theselected dataline 160 along with the reference dataline 161 are input toa sense amplifier 140 to generate an output Q0. In this embodiment, eachWLRBi and WLBi (i=0, 1, . . . , n−1) are hardwired together and everycells in the reference columns need to be pre-programmed before read.

FIG. 17( b) shows another embodiment of using a reference cell externalto a reference column. In FIG. 17( b), a portion of memory 400 has anormal array 180 of n×m cells, a reference column 150 of n×1 cells, m+1Y-read pass gates 130, and a sense amplifier 140. When a wordline WLBi(i=0, 1, . . . , n−1) is turned on, none of the cells in the referencecolumn 150 are turned on. An external reference cell 170 with apre-determined resistance is turned on instead by an external referencewordline WLRB. The selected dataline 160 and the reference dataline 161are input to a sense amplifier 140 to generate an output Q0. In thisembodiment, all internal reference wordlines WLRBi (i=0, 1, . . . , n−1)in each row are disabled. The reference column 150 provides a loading tomatch with that of the normal columns. The reference cells or thereference column 150 can be omitted in other embodiments.

FIG. 17( c) shows another embodiment of constructing reference cells fordifferential sensing. In FIG. 17( c), a portion of memory 400 has anormal array 180 of n×m cells, one reference column 150 of n×1, tworeference rows 175-0 and 175-1 of 1×m cells, m+1 Y-read pass gates 130,and a sense amplifier 140. As an example, n=8 and m=8 are used toillustrate the approach. There are n wordlines WLBi and 2 referencewordlines WLRB0 175-0 and WLRB1 175-1 on top and bottom of the array,where i=0, 1, . . . , n−1. When a wordline WLBi (i=0, 1, . . . , n−1) isturned on to access a row, the reference wordline WLRB0 and WLRB1 arealso turned on to activate two reference cells 170-0 and 170-1 in theupper and lower right corners of the array 180, which store data 0 and 1respectively. The selected dataline 160 along with the referencedataline 161 are input to a sense amplifier 140 to generate an outputQ0. In this embodiment, all cells in the reference column 150 aredisabled except that the cells 170-0 and 170-1 on top and bottom of thereference column 150. Only two reference cells are used for the entiren×m array that needs to be pre-programmed before read.

For those programmable resistive devices that have a very smallresistance ratio between states 1 and 0, such as 2:1 ratio in MRAM,FIGS. 17( a) and 17(c) are desirable embodiments, depending on how manycells are suitable for one pair of reference cells. Otherwise, FIG. 17(b) is a desirable embodiment for electrical fuse or PCM that hasresistance ratio of more than about 10.

FIGS. 15, 16(a), 16(b), 17(a), 17(b), and 17(c) show only a fewembodiments of a portion of programmable resistive memory in asimplified manner. The memory array 101 in FIGS. 15, 16(a), and 16(b)can be replicated s times to read or program s-cells at the same time.In the case of differential sensing, the number of reference columns tonormal columns may vary and the physical location can also vary relativeto the normal data columns. Rows and columns are interchangeable. Thenumbers of rows, columns, or cells likewise may vary. For those skilledin the art understand that the above descriptions are for illustrativepurpose. Various embodiments of array structures, configurations, andcircuits are possible and are still within the scope of this invention.

The portions of programmable resistive memories shown in FIGS. 15,16(a), 16(b), 17(a), 17(b) and 17(c) can include different types ofresistive elements. The resistive element can be an electrical fuseincluding a fuse fabricated from an interconnect, contact/via fuse,contact/via anti-fuse, or gate oxide breakdown anti-fuse. Theinterconnect fuse can be formed from silicide, polysilicon, silicidedpolysilicon, metal, metal alloy, local interconnect, metal-0, thermallyisolated active region, or some combination thereof, or can beconstructed from a CMOS gate. The resistive element can also befabricated from phase-change material in PCRAM, resistive film inRRAM/CBRAM, or MTJ in MRAM, etc. For the electrical fuse fabricated froman interconnect, contact, or via fuse, programming requirement is toprovide a sufficiently high current, about 4-20 mA range, for a fewmicroseconds to blow the fuse by electro-migration, heat, ion diffusion,or some combination thereof. For anti-fuse, programming requirement isto provide a sufficiently high voltage to breakdown the dielectricsbetween two ends of a contact, via or CMOS gate/body. The requiredvoltage is about 6-7V for a few millisecond to consume about 100 uA ofcurrent in today's technologies. Programming Phase-Change Memory (PCM)requires different voltages and durations for 0 and 1. Programming to a1 (or to reset) requires a high and short voltage pulse applied to thephase-change film. Alternatively, programming to a 0 (or to set)requires a low and long voltage pulse applied to the phase change film.The reset needs about 3V for 50 ns and consumes about 300 uA, while setneeds about 2V for 300 ns and consumes about 100 uA. For MRAM, the highand low program voltages are about 2-3V and 0V, respectively, and thecurrent is about +/−100-200 uA.

Most programmable resistive devices have a higher voltage VDDP (˜2-3V)for programming than the core logic supply voltage VDD (˜1.0V) forreading. FIG. 18( a) shows a schematic of a wordline driver circuit 60according to one embodiment. The wordline driver includes devices 62 and61, as shown as the wordline driver 150 in FIGS. 15, 16(a) and 16(b).The supply voltage vddi is further coupled to either VDDP or VDD throughpower selectors 63 and 64 (e.g., PMOS power selectors) respectively. Theinput of the wordline driver Vin is from an output of an X-decoder. Insome embodiments, the power selectors 63 and 64 are implemented as thickoxide I/O devices to sustain high voltage. The bodies of power selector63 and 64 can be tied to vddi to prevent latchup.

Similarly, bitlines tend to have a higher voltage VDDP (˜2-3V) forprogramming than the core logic supply voltage VDD (˜1.0V) for reading.FIG. 18( b) shows a schematic of a bitline circuit 70 according to oneembodiment. The bitline circuit 70 includes a bitline (BL) coupled toVDDP and VDD through power selectors 73 and 74 (e.g., PMOS powerselectors), respectively. If the bitline needs to sink a current such asin an MRAM, an NMOS pulldown device 71 can be provided. In someembodiments, the power selectors 73 and 74 as well as the pulldowndevice 71 can be implemented as thick-oxide I/O devices to sustain highvoltage. The bodies of power selector 73 and 74 can be tied to vddi toprevent latchup.

Using junction diodes as program selectors may have high leakage currentif a memory size is very large. Power selectors for a memory can helpreducing leakage current by switching to a lower supply voltage or eventurning off when a portion of memory is not in use. FIG. 18( c) shows aportion of memory 85 with an internal power supply VDDP coupled to anexternal supply VDDPP and a core logic supply VDD through powerselectors 83 and 84. VDDP can even be coupled to ground by an NMOSpulldown device 81 to disable this portion of memory 85, if this portionof memory is temporarily not in use.

FIG. 19( a) shows one embodiment of a schematic of a pre-amplifier 100according to one embodiment. The pre-amplifier 100 needs specialconsiderations because the supply voltage VDD for core logic devices isabout 1.0V that does not have enough head room to turn on a diode tomake sense amplifiers functional, considering a diode's threshold isabout 0.7V. One embodiment is to use another supply VDDR, higher thanVDD, to power at least the first stage of sense amplifiers. Theprogrammable resistive cell 110 shown in FIG. 19( a) has a resistiveelement 111 and a diode 112 as program selector, and can be selected forread by asserting YSR′ to turn on a gate of a MOS 130 and wordline barWLB. The MOS 130 is a Y-select pass gate to select a signal from one ofthe at least one bitline(s) (BL) coupled to cells to a dataline (DL) forsensing. The pre-amplifier 100 also has a reference cell 115 including areference resistive element 116 and a reference diode 117. The referencecell 115 can be selected for differential sensing by asserting YSRR′ toturn on a gate of a MOS 131 and reference wordline WLRB. The MOS 131 isa reference pass gate to pass a signal from a reference bitline (BLR) toa reference dataline (DLR) for sensing. YSRR′ is similar to YSR′ to turnon a reference cell rather than a selected cell, except that thereference branch typically has only one reference bitline (BLR). Theresistance Ref of the reference resistive element 116 can be set at aresistance approximately half-way between the minimum of state 1 andmaximum of state 0 resistance. MOS 151 is for pre-charging DL and DLR tothe same voltage before sensing by a pre-charge signal Vpc.Alternatively, the DL or DLR can be pre-charged to each other or to adiode voltage above ground in other embodiments. The reference resistorelement 116 can be a plurality of resistors for selection to suitdifferent cell resistance ranges in another embodiment.

The drains of MOS 130 and 131 are coupled to sources of NMOS 132 and134, respectively. The gates of 132 and 134 are biased at a fixedvoltage Vbias. The channel width to length ratios of NMOS 132 and 134can be relatively large to clamp the voltage swings of dataline DL andreference dataline DLR, respectively. The drain of NMOS 132 and 134 arecoupled to drains of PMOS 170 and 171, respectively. The drain of PMOS170 is coupled to the gate of PMOS 171 and the drain of PMOS 171 iscoupled to the gate of PMOS 170. The outputs V+ and V− of thepre-amplifier 100 are the drains of PMOS 170 and PMOS 171 respectively.The sources of PMOS 170 and PMOS 171 are coupled to a read supplyvoltage VDDR. The outputs V+ and V− are pulled up by a pair of PMOS 175to VDDR when the pre-amplifier 100 is disabled. VDDR is about 2-3V(which is higher than about 1.0V VDD of core logic devices) to turn onthe diode selectors 112 and 117 in the programmable resistive cell 110and the reference cell 115, respectively. The CMOS 130, 131, 132, 134,170, 171, and 175 can be embodied as thick-oxide I/O devices to sustainhigh voltage VDDR. The NMOS 132 and 134 can be native NMOS (i.e., thethreshold voltage is ˜0V) to allow operating at a lower VDDR. In anotherembodiment, the read selectors 130 and 131 can be PMOS devices. Inanother embodiment, the sources of PMOS 170 and 171 can be coupled tothe drain of a PMOS pullup (an activation device not shown in FIG. 19(a)), whose source is then coupled to VDDR. This sense amplifier can beactivated by setting the gate of the PMOS pullup low after turning onthe reference and Y-select pass gates.

FIG. 19( b) shows one embodiment of a schematic of an amplifier 200according to one embodiment. In another embodiment, the outputs V+ andV− of the pre-amplifier 100 in FIG. 19( a) can be coupled to gates ofNMOS 234 and 232, respectively, of the amplifier 200. The NMOS 234 and232 can be relatively thick oxide I/O devices to sustain the high inputvoltage V+ and V− from a pre-amplifier. The sources of NMOS 234 and 232are coupled to drains of NMOS 231 and 230, respectively. The sources ofNMOS 231 and 230 are coupled to a drain of an NMOS 211. The gate of NMOS211 is coupled to a clock φ to turn on the amplifier 200, while thesource of NMOS 211 is coupled to ground. The drains of NMOS 234 and 232are coupled to drains of PMOS 271 and 270, respectively. The sources ofPMOS 271 and 270 are coupled to a core logic supply VDD. The gates ofPMOS 271 and NMOS 231 are connected and coupled to the drain of PMOS270, as a node Vp. Similarly, the gates of PMOS 270 and NMOS 230 areconnected and coupled to the drain of PMOS 271, as a node Vn. The nodesVp and Vn are pulled up by a pair of PMOS 275 to VDD when the amplifier200 is disabled when φ goes low. The output nodes Vout+ and Vout− arecoupled to nodes Vn and Vp through a pair of inverters as buffers.

FIG. 19( c) shows a timing diagram of the pre-amplifier 100 and theamplifier 200 in FIGS. 19( a) and 19(b), respectively. The X- andY-addresses AX/AY are selected to read a cell. After some propagationdelays, a cell is selected for read by turning WLB low and YSR high tothereby select a row and a column, respectively. Before activating thepre-amplifier 100, a pulse Vpc can be generated to precharge DL and DLRto ground, to a diode voltage above ground, or to each other. Thepre-amplifier 100 would be very slow if the DL and DLR voltages are highenough to turn off the cascode devices (e.g., NMOS 132 and 134). Afterthe pre-amplifier outputs V+ and V− are stabilized, the clock φ is sethigh to turn on the amplifier 200 and to amplify the final output Vout+and Vout− into full logic levels. The precharge scheme can be omitted inother embodiments.

FIG. 20( a) shows another embodiment of a pre-amplifier 100′, similar tothe pre-amplifier 100 in FIG. 19( a), with PMOS pull-ups 171 and 170configured as current mirror loads. The reference branch can be turnedon by a level signal, Sense Amplifier Enable (SAEN), to enable thepre-amplifier, or by a cycle-by-cycle signal YSRR′ as in FIG. 19( a).MOS 151 is for pre-charging DL and DLR to the same voltage beforesensing by a pre-charge signal Vpc. Alternatively, the DL or DLR can bepre-charged to ground or to a diode voltage above ground in otherembodiments. In this embodiment, the number of the reference branchescan be shared between different pre-amplifiers at the expense ofincreasing power consumption. The reference resistor 116 can be aplurality of resistors for selection to suit different cell resistanceranges in another embodiment.

FIG. 20( b) shows level shifters 300 according to one embodiment. The V+and V− from the pre-amplifier 100, 100′ outputs in FIG. 19( a) or FIG.20( a) are coupled to gates of NMOS 301 and 302, respectively. Thedrains of NMOS 301 and 302 are coupled to a supply voltage VDDR. Thesources of NMOS 301 and 302 are coupled to drains of NMOS 303 and 304,respectively, which have gates and drains connected as diodes to shiftthe voltage level down by one Vtn, the threshold voltage of an NMOS. Thesources of NMOS 303 and 304 are coupled to the drains of pulldowndevices NMOS 305 and 306, respectively. The gates of NMOS 305 and 306can be turned on by a clock φ. The NMOS 301, 302, 303 and 304 can bethick-oxide I/O devices to sustain high voltage VDDR. The NMOS 303 and304 can be cascaded more than once to shift V+ and V− further to propervoltage levels Vp and Vn. In another embodiment, the level shiftingdevices 303 and 304 can be built using PMOS devices.

FIG. 20( c) shows another embodiment of an amplifier 200′ withcurrent-mirror loads having PMOS 270 and 271 as loads. The inputs Vp andVn of the amplifier 200′ are from the outputs Vp and Vn of the levelshifter 300 in FIG. 20( b) that can be coupled to gates of NMOS 231 and230, respectively. The drains of NMOS 231 and 230 are coupled to drainsof PMOS 271 and 270 which provide current-mirror loads. The drain andgate of PMOS 271 are connected and coupled to the gate of PMOS 270. Thesources of NMOS 231 and 230 are coupled to the drain of an NMOS 211,which has the gate coupled to a clock signal φ and the source to ground.The clock signal φ enables the amplifier 200′. The drain of PMOS 270provides an output Vout+. The PMOS pullup 275 keeps the output Vout+ atlogic high level when the amplifier 200′ is disabled.

FIG. 20( d) shows one embodiment of a pre-amplifier 100′ based on allcore devices according to one embodiment. The programmable resistivecell 110′ has a resistive element 111′ and a diode 112′ as programselector that can be selected for read by asserting YSR′ to turn on agate of a MOS 130′ and wordline bar WLB. The MOS 130′ is a Y-select passgate to select a signal from one of the at least one bitline(s) (BL)coupled to cells to a dataline (DL) for sensing. The pre-amplifier 100′also has a reference cell 115′ including a reference resistive element116′ and a reference diode 117′. The reference resistor 116′ can be aplurality of resistors for selection to suit different cell resistanceranges in another embodiment. The reference cell 115′ can be selectedfor differential sensing by asserting YSRR′ to turn on a gate of a MOS131′ and reference wordline WLRB. The MOS 131′ is a reference pass gateto pass a signal from a reference bitline (BLR) to a reference dataline(DLR) for sensing. YSRR′ is similar to YSR′ to turn on a reference cellrather than a selected cell, except that the reference branch typicallyhas only one reference bitline (BLR). The drains of MOS 130′ and 131′are coupled to drains of PMOS 170′ and 171′, respectively. The gate of170′ is coupled to the drain of 171′ and the gate of 171′ is coupled tothe drain of 170′. The sources of MOS 170′ and 171′ are coupled to thedrains of MOS 276′ and 275′, respectively. The gate of 275′ is coupledto the drain of 276′ and the gate of 276′ is coupled to the drain of275′. The drains of 170′ and 171′ are coupled by a MOS equalizer 151′with a gate controlled by an equalizer signal Veq1. The drains of 276′and 275′ are coupled by a MOS equalizer 251′ with a gate controlled byan equalizer signal Veq0. The equalizer signals Veq0 and Veq1 can be dcor ac signals to reduce the voltage swing in the drains of 170′, 171′and 275′, 276′, respectively. By reducing the voltage swings of the PMOSdevices in the pullup and by stacking more than one level ofcross-coupled PMOS, the voltage swings of the 170′, 171′, 275′, and 276′can be reduced to VDD range so that core logic devices can be used. Forexample, the supply voltage of the sense amplifier VDDR is about 2.5V,while the VDD for core logic devices is about 1.0V. The DL and DLR areabout 1 V, based on diode voltage of about 0.7V with a few hundredmillivolts drop for resistors and pass gates. If the cross-coupled PMOSare in two-level stacks, each PMOS only endures voltage stress of(2.5-1.0)/2=0.75V. Alternatively, merging MOS 275′ and 276′ into asingle MOS or using a junction diode in the pullup is anotherembodiment. Inserting low-Vt NMOS as cascode devices between 170′ and130′; 171′ and 131′ is another embodiment. The output nodes from thedrains of 170′ and 171′ are about 1.0-1.2V so that the sense amplifieras shown in FIG. 19( b) can be used with all core logic devices.

FIG. 20( e) shows another embodiment of a pre-amplifier 100″ with anactivation device 275″ according to one embodiment. The programmableresistive cell 110″ has a resistive element 111″ and a diode 112″ asprogram selector that can be selected for read by asserting YSR″ to turnon a gate of a MOS 130″ and wordline bar WLB. The MOS 130″ is a Y-selectpass gate to select a signal from one of the at least one bitline(s)(BL) coupled to cells to a dataline (DL) for sensing. The pre-amplifier100″ also has a reference cell 115″ including a reference resistiveelement 116″ and a reference diode 117″. The reference resistor 116 canbe a plurality of resistors to suit different cell resistance ranges inanother embodiment. The reference cell 115″ can be selected fordifferential sensing by asserting YSRR″ to turn on a gate of a MOS 131″and reference wordline WLRB. The MOS 131″ is a reference pass gate topass a signal from a reference bitline (BLR) to a reference dataline(DLR) for sensing. YSRR″ is similar to YSR″ to turn on a reference cellrather than a selected cell, except that the reference branch typicallyhas only one reference bitline (BLR). The drains of MOS 130″ and 131″are coupled to the sources of MOS 132″ and 134″, respectively. Thedrains of MOS 132″ and 134″ are coupled to the drains of PMOS 170″ and171″, respectively. The gate of 170″ is coupled to the drain of 171″ andthe gate of 171″ is coupled to the drain of 170″. The sources of MOS170″ and 171″ are coupled to the drain of MOS 275″ whose source iscoupled to a supply voltage and gate coupled to a Sensing Enable Bar(SEB). The drains of 170″ and 171″ are coupled by a MOS equalizer 251″with a gate controlled by an equalizer signal Veq0. The sources of 132″and 134″ are coupled by a MOS equalizer 151″ with a gate controlled byan equalizer signal Veq1. The equalizer signals Veq0 and Veq1 can be dcor ac signals to reduce the voltage swings in the sources of 170″, 171″and 132″, 134″, respectively.

FIGS. 19( a), 20(a), 20(d) and 20(e) only show four of manypre-amplifier embodiments. Similarly, FIGS. 19( b), 20(c) and 20(b) onlyshow several of many amplifier and level shifter embodiments. Variouscombinations of pre-amplifiers, level shifters, and amplifiers in NMOSor PMOS, in core logic or I/O devices, with devices stacked or with anactivation device, operated under high voltage VDDR or core supply VDDcan be constructed differently, separately, or mixed. The equalizerdevices can be embodied as PMOS or NMOS, and can be activated by a dc orac signal. In some embodiments, the precharge or equalizer technique canbe omitted.

FIGS. 21( a) and 21(b) show a flow chart depicting embodiments of aprogram method 700 and a read method 800, respectively, for aprogrammable resistive memory in accordance with certain embodiments.The methods 700 and 800 are described in the context of a programmableresistive memory, such as the programmable resistive memory 100 in FIGS.15, 16(a) and 16(b). In addition, although described as a flow of steps,one of ordinary skilled in the art will recognize that at least some ofthe steps may be performed in a different order, includingsimultaneously, or skipped.

FIG. 21( a) depicts a method 700 of programming a programmable resistivememory in a flow chart according to one embodiment. In the first step710, proper power selectors can be selected so that high voltages can beapplied to the power supplies of wordline drivers and bitlines. In thesecond step 720, the data to be programmed in a control logic (not shownin FIGS. 15, 16(a), and 16(b)) can be analyzed, depending on what typesof programmable resistive devices. For electrical fuse, this is aOne-Time-Programmable (OTP) device such that programming always meansblowing fuses into a non-virgin state and is irreversible. Programvoltage and duration tend to be determined by external control signals,rather than generated internally from the memory. For PCM, programminginto a 1 (to reset) and programming into a 0 (to set) require differentvoltages and durations such that a control logic determines the inputdata and select proper power selectors and assert control signals withproper timings. For MRAM, the directions of current flowing through MTJsare more important than time duration. A control logic determines properpower selectors for wordlines and bitlines and assert control signals toensure a current flowing in the desired direction for desired time. Inthe third step 730, a cell in a row can be selected and thecorresponding local wordline can be turned on. In the fourth step 740,sense amplifiers can be disabled to save power and prevent interferencewith the program operations. In the fifth step 750, a cell in a columncan be selected and the corresponding Y-write pass gate can be turned onto couple the selected bitline to a supply voltage. In the last step760, a desired current can be driven for a desired time in anestablished conduction path to complete the program operations. For mostprogrammable resistive memories, this conduction path is from a highvoltage supply through a bitline select, resistive element, diode asprogram selector, and an NMOS pulldown of a local wordline driver toground. Particularly, for programming a 1 to an MRAM, the conductionpath is from a high voltage supply through a PMOS pullup of a localwordline driver, diode as program selector, resistive element, andbitline select to ground.

FIG. 21( b) depicts a method 800 of reading a programmable resistivememory in a flow chart according to one embodiment. In the first step810, proper power selectors can be selected to provide supply voltagesfor local wordline drivers, sense amplifiers, and other circuits. In thesecond step 820, all Y-write pass gates, i.e., bitline programselectors, can be disabled. In the third step 830, desired localwordline(s) can be selected so that the diode(s) as program selector(s)have a conduction path to ground. In the fourth step 840, senseamplifiers can be enabled and prepared for sensing incoming signals. Inthe fifth step 850, the dataline and the reference dataline can bepre-charged to the V− voltage of the programmable resistive device cell.In the sixth step 860, the desired Y-read pass gate can be selected sothat the desired bitline is coupled to an input of the sense amplifier.A conduction path is thus established from the bitline to the resistiveelement in the desired cell, diode(s) as program selector(s), and thepulldown of the local wordline driver(s) to ground. The same applies forthe reference branch. In the last step 870, the sense amplifiers cancompare the read current with the reference current to determine a logicoutput of 0 or 1 to complete the read operations.

FIG. 22 shows a processor system 700 according to one embodiment. Theprocessor system 700 can include a programmable resistive device 744,such as in a cell array 742, in memory 740, according to one embodiment.The processor system 700 can, for example, pertain to a computer system.The computer system can include a Central Process Unit (CPU) 710, whichcommunicate through a common bus 715 to various memory and peripheraldevices such as I/O 720, hard disk drive 730, CDROM 750, memory 740, andother memory 760. Other memory 760 is a conventional memory such asSRAM, DRAM, or flash, typically interfaces to CPU 710 through a memorycontroller. CPU 710 generally is a microprocessor, a digital signalprocessor, or other programmable digital logic devices. Memory 740 ispreferably constructed as an integrated circuit, which includes thememory array 742 having at least one programmable resistive device 744.The memory 740 typically interfaces to CPU 710 through a memorycontroller. If desired, the memory 740 may be combined with theprocessor, for example CPU 710, in a single integrated circuit.

The invention can be implemented in a part or all of an integratedcircuit in a Printed Circuit Board (PCB), or in a system. Theprogrammable resistive device can be fuse, anti-fuse, or emergingnonvolatile memory. The fuse can be silicided or non-silicidedpolysilicon fuse, thermally isolated active-region fuse, localinterconnect fuse, metal-0 fuse, metal fuse, contact fuse, via fuse, orfuse constructed from CMOS gates. The anti-fuse can be a gate-oxidebreakdown anti-fuse, contact or via anti-fuse with dielectricsin-between. The emerging nonvolatile memory can be Magnetic RAM (MRAM),Phase Change Memory (PCM), Conductive Bridge RAM (CBRAM), or ResistiveRAM (RRAM). Though the program mechanisms are different, their logicstates can be distinguished by different resistance values.

The above description and drawings are only to be consideredillustrative of exemplary embodiments, which achieve the features andadvantages of the present invention. Modifications and substitutions ofspecific process conditions and structures can be made without departingfrom the spirit and scope of the present invention.

The many features and advantages of the present invention are apparentfrom the written description and, thus, it is intended by the appendedclaims to cover all such features and advantages of the invention.Further, since numerous modifications and changes will readily occur tothose skilled in the art, it is not desired to limit the invention tothe exact construction and operation as illustrated and described.Hence, all suitable modifications and equivalents may be resorted to asfalling within the scope of the invention.

1. A One-Time Programmable (OTP) memory, comprising: a plurality of OTPcells, at least one of the cells comprising: an OTP element coupled to afirst supply voltage line; a diode including at least a first activeregion and a second active region isolated from the first active region,where the first active region having a first type of dopant and a secondactive region having a second type of dopant, the first active regionproviding a first terminal of the diode, the second active regionproviding a second terminal of the diode, both the first and secondactive regions residing in a common CMOS well or on an isolatedsubstrate, the first active region coupled to the OTP element and thesecond active region coupled to a second supply voltage line; and atleast one thermally conductive element, coupled to the OTP element, todissipate or generate heat, wherein the OTP element is configured to beprogrammable by applying voltages to the first and the second supplyvoltage lines to thereby change its logic state, and wherein thethermally conductive element is configured to assist in programming ofthe OTP element.